Noveria neutron purge question

Han Olar can live even if you set off the Neutron Purge first... just go down there right after Ventrallis' men attack you and you'll find him being held at gunpoint by an Asari commando.  She'll turn hostile towards Shepard after a cut scene and you'll have to kill her, along with the other two scientists who told Olar to be quiet earlier.  Olar, however, will not become hostile and you can talk to him afterward.  He will say something to the effect - "Everywhere I go I'm the only survivor."

If you do the purge first and confront Ventralis, he will say "I'm sorry Shepard, we have orders from Benezia..." It's unclear to me whether that situation changes just because you do the purge second... Before doing the purge, Dr. Cohen can indicate to you that the guards have been acting strangely since Shepard arrived and that he thinks they were expecting Shepard.  This indicates to me that they are possibly on Benezia's side regardless of when you do the purge.  If you kill Benezia first, you are automatically locked out of the living area before doing the purge... indicating to me that, perhaps, Ventrallis and his men have already killed everyone else at that point.

There are another options even when you do the purge second... 1) You can head to Benezia's area through the maintenance area (near where Han Olar is standing) and kill one rachni and not fight any guards or 2) you can bypass Benezia and fight your way up to where the scientists are... in which case everyone in that area will be hostile towards you and you'll be forced to kill them all yourself.  3) IYou can also just open fire on the drones guarding that area and hack the door... in which case all the scientists become hostile.

If you then go down to see Olar, however, you get the same scene as I described and Shepard will still imply that it was Ventralis' men who was killing everyone.

In my opinion, the whole level is organized very chaotically and is somewhat bugg (unless they fixed some things in MELE that I don't know about yet because I haven't run through it in all possible ways yet).

My own preference is to do the purge first... falling for Ventrallis' trap and once you're down there, the only way out is to use the purge and then Ventrallis attacks you after he and his men have killed all the scientists except Han Olar... who you can save (which is a paragon thing to do).

However, Ventrallis is always under Benezia's command regardless.  He clearly lies to you about her location right from the start since he tells you she's in the Hot Labs when she is at Rift Station all along.  Also, everyone in that facility works for Saren and Benezia since Saren is a major investor in Binary Helix.  As I said, Olar can survive even if you do the purge first, so I'm not assuming that not doing the purge first means that everyone else lives regardless.  You cannot enter the area once you kill Benezia, so I'm assuming that while you're off killing Benezia, Ventrallis and his guards are inside the now locked living area and are killing everyone but Olar anyways.  The only way Olar dies is if you do the purge first and then don't go down to help him get free from the Asari commando (and I'm not even sure he dies then... it's been a long time since I've not saved him so I can't remember whether or not you still get the email in ME2).

Ventrallis is a bad person who is lying to you regardless.  How does Alestia find out that you're locked into the lab? It's pretty obvious that Ventrallis tells her that after you ask permission from him to go in there and he sets the condition that you be locked in there.  The guard that Alestia kills is not on Ventrallis' side because he know you're down there to make a cure... but the other two reveal themselves to be on Ventrallis' side when you go to save Olar since they become hostile, along with the Asari commando who was holding a gun on Olar.

It's vague enough that you can head canon that Ventrallis is a good guy... but the level is clearly written in such a way that he is not.  All the scientists, except Olar, die regardless.  Ventrallis and his men kill them because, as Olar can tell you, they know too much.  It is also Ventrallis who is preventing Cohen from going into the area to get the cure himself... why? because Ventrallis wants those scientists to die... again, because they know too much.  I don't think it is more paragon to let him get away with that and any soldier who helps him deserves to die as well.

I'm afraid ONLY Han Olar survives regardless.  Ventralis and his men kill the other scientists.  It's verified when you encounter the Asari holding a gun on Olar in the science team's quarters (and Olar says "Everywhere I go, I"m the only survivor." and it's verified in Olar's ME2 emai (which is the same regardless of whether you actually saw the Asari holding a gun on Olar or not)l:

The "they" being referred to in the lines I've highlighted are Olar's psychiatrists... not the other scientists.

... but you can convince yourself otherwise if you want to.

The fact remains that you receive the EXACT same email even if you find Olar and he tells you "Everywhere I go I'm the ONLY survivor."  You can even ask him then "Why they (Ventralis and his men) are killing the scientists."  It's clear to me that the writers of the level did not make an actual provision for a situation where the scientists could be saved.  Had they done that, the email received would have been different from the one received when it's clear that only Olar survives.

As I said... you can convince yourself otherwise if you want to.  It's imprecise writing... which is the same "technique" used throughout the entire trilogy to enable the player to head canon whatever they like.