Superpenguin
Penguins! <3
A decent theory and it's great that you brought this to attention. However, I want to point out that the EXALT Rookie has no special powers and that EXALT doesn't have KP (Right?) - So the newly converted scum member isn't exactly a major threat. Let's just take everything Aerious says with a grain of salt. (I kind of already did anyways..)
Let's talk about the Night Kills. Three people dead. The EXALT team only had one killing action to use on Night 1 I believe - The rocket launcher strike. It's possible that one of the three kills was indeed made by that, but it's surprising that there was no splash casualties in that case. It's more like that all three were made by the Aliens, and it's also possible that a fourth person was implanted with an embryo by the Chryssalid.
This could mean that we're looking at SIX Aliens (KP of 3) - One of which is probably the Chryssalid (If there is one in the game). With the new EXALT Rookie, and judging from the game size, I would guess they're probably at least 4 or 5 on that team too. This leads me to feel that going after an XCOM Rookie who might've been converted to an EXALT Rookie should not be the top priority for todays lynch. However, having a Vig take Aerious out if they continue to seem suspicious is probably not a bad idea.
Then how about finding another player who is suspicious.