I'm doing this question because in some ways I feel that maybe me and my group has misinterpreted the rules...

Does a Black templar with the Abhor the Witch talent would be invulnerable to the Vortex of Doom power and all of it's effects or there are things that Abhor the Witch doesn't cover regarding psychic powers, meaning that although being immune to the psychic power, there are some effects that originate from the power but the talent doesn't make you immune???

Please analyze the situation and throw me some clarity here regarding that special case...

I don't have any books handy right now, but what I usually see is that immunity only applies to effects directed specifically at that character. Since the vortex is technically outside the templar, I would think he's not safe from it. I guess it depends on where you draw the line between the power itself and a more general warp effect.

I could see this getting very semantic.

Per page 113:

"The effects of this Talent also apply to powers that cause Damage indirectly such as blasts, and those used by friendly psychers which might be beneficial to the Battle-Brother."

So the that reads to me that not only direct damage such as Smite, but any damage or effect due to psychic powers stands a chance through a Challenging (+0) Willpower test to be blocked by Abhor the Witch... Stinking Black Templars...