Actually, its funny that this post just got revived...
We finally went out and got a Python gravel vac a few weeks back and the cleaning power is incredible! (BTW, I can see underneath my UGF and there is barely any buildup of anything under there since I've been using the Python!
Highly reccommend it.)
So anyway, there was this slate rock that was in the tank (previous owner donation) and I had checked/ cleaned underneath it a few times, but last weekend I decided to take it out altogether. (It's very heavy and I always worry I'm going to drop it when I move it around the tank.) Well, when I vacuumed in that spot with the Python, it pulled something up from the gravel and sent it through the tube to the sink. We "fished it out" (excuse the pun) of the sink and I'm 95% sure its the skeleton of the missing oto.
And yes, Barbrella, I did check the filter box, because I has the same thought!
Thanks for the help guys!