I'm pretty sure the 88 and the 90 will capture the altitude in VNav even if the ALT is not armed. I don't attempt to do this on a regular basis, nor would I recommend it to my buddies.

I don't think either will capture altitude in VS or IAS mode if the ALT isn't armed, but I haven't played around on the 90 enough to act like I'm an expert.

I do watch the FMA like an expert when approaching an altitude, no matter what I'm flying.