Can inquisitors be members of the temple tendency? i know it'd be improbable, what with the whole Apostate problem, but could it happen?

Of course an Inquisitor would need to keep it a secret…but basically it is just anohter form of Radicalismn. The Heresy the Inquisititor begets is just of another type. Actually, the RH offers PC the option to be a Heretic. The Temple Tendency is a heresy, so it is all fair game

While Inquisitors can be members, and the Tendency would probably be very happy wiith a coup like that, they will of course be irredemable heretics as defined by the Imperium. Not as bad as followers of Chaos to be sure but bad enough to be killed without a second thought.

I have to agree, in fact I had a Throne Agent in an Ascension game I ran who was a member of the Temple Tendency. Kind of fun since we used the Apostasy Gambit scenarios (well the first two) and he was quite pleased in secret to help bring about the downfall of some of the usurpers. He of course kept this very quiet! Then again that group of throne agents and their Inquisitor were a bit radical, not lets use daemon weapons but in other ways such as the Primaris Psyker from Dusk who evaluated things on whether they should be killed by A) Is it a Daemon, B) Trying to kill me… anything else was negotiable when it came to dealings.