Latency differences between amplifiers? Not unless they do signal processing of some sort. If you're just talking about a run-of-the-mill analog amplifier latency is a non-issue.
Sensitivity variance is a very real and important consideration, even for amps of the same model from the same manufacturer. The amps need to be matched to a fraction of a decibel, and gets complicated if you're going to use horizontal bi-amping, because you'll have different amps on the same channel. At least with vertical bi-amping you might be able to solve some problems with a balance control, assuming you even have a balance control.
For the most part, IMO, passive bi-amping is a waste of money. If you have very complex, power-hungry multi-driver speakers with complicated crossovers you might get an audible benefit, but unless you have a special situation I wouldn't bother.
Active crossovers with multi-amping is the best way to build a multi-driver speaker, but so few are available in the market. One that comes to mind is the Linkwitz Orion. Another is the Legacy Audio Helix.
