I actually kinda thought 4-2-5 was a nickel defense...
But really, the defensive front is what I'm interested in. I know we did weird things with our DB/LB/"PB"s lats year. But sliding a DT out to DE, and moving a DE to stand-up outside linebacker, is the basic principle that screams "3-4 front" to me, so I don't know if it's too unfair to call it that, with our odd defensive backfields package as a caveat. I did not realize we did this against Missouri. Cam was a strongside(?) linebacker? And Crick as one of the DEs with Stein as NT? Technically, I guess you are right, it's a 3-2-6 - or a 3-3-5 is the peso is considered a linebacker (I always considered it just...nickelback).
But if we run a base 4-3 this year as claimed by the coaches, and I don't see why we wouldn't, then showing that kind of 3-man front look results in a true 3-4 front. Which gives some promise to the idea of some 3-4 being run this year. I'm sure we've done wacky stuff before, like 5 down linemen or 1 down lineman, but I don't think that (or the 3-4 variability) makes us into a 3-4 team. I think we'll run out of a 4-3 base still with a 4-man front. The Pats are a committed 3-4 team, but they showed 4-man front looks often last year.
(EDIT), or not! After looking at the brophog post that druski linked to, even what we did with our DL personnel was just flat out weird. I didn't think Allen was really stout enough to be 3-4 DE material and as it turns out, they had him playing in the middle. The nose? And kicked out BOTH DTs outside the edge, lining them up outside the tackles apparently, to stop runs. Didn't read what Meredith's role was, possibly run support. Anyway, it seems very innovative and far too out-of-the-box to label as a 3-4, and also pitter-patters the possibility that we'll do that again this year outside of special situational circumstances. Two DTs outside the tackles...man, do we have some outstanding defensive coaches or what!