Iunno about that, Aigis didn't really sense much about Ryoji except that she didn't trust him, and Ryoji was both very powerful and a Shadow that Aigis had met before, and it's suggested that that sense of familiarity with Thanatos was the only reason she suspected anything...and even then, it wasn't really enough to act on, she just somehow knew he was dangerous. And, frankly, Teddie seems somewhat like Ryoji in that regard, and his body seems perfectly human, beyond the inability of x-rays to peer into it, so, I would suspect that, at most, she might sense something a little odd with him.
Then again, it should also be remembered that a Persona-user has the power of their Shadow under the control of their ego, and it's indisputable that Teddie, unlike Shadows, has an ego. Which his form is presumably under the control of. So she might not sense anything off about him, at least not more than any persona-user...hard to say, though. But, Rise can sense powerful shadows at a minimum, and after you work on her Social Rank, shadows in the nearby vicinity, and as I recall, Teddie's always marked as an ally, which would presumably be a persona-user, and never as a Shadow...though, how much that says is debatable.
Then again, Teddie's something of a freak as Shadows go...it was stated that the presence of a persona-user drives Shadows nuts, but he was always unaffected by any desire to kill his beloved sensei...so, I'm not sure if I buy that he was 'just' another Shadow. Plus, when Shadow Teddie popped out, Rise said she sensed something else mucking about...always wondered about that, since I have my doubts it would have been Izanami.