Any other issues with running two alternators to two connected batteries that I’m overlooking? No other problems in the last 4 years. I do know that a bad cell on one battery can take out the other but I keep a close eye on them to be sure the voltage of each remains the same.
Given you've been operating this way for four years without apparent problems, it may be moot, but you're probably only drawing apreciable charge current on one alternator. Upon energizing, the first alternator in your battery system that gets direction from it's regulator to begin charging will take on 100% of the charge duties for both batteries. The second alternator on the other engine will simply loaf along. It is likely that the 2nd alternator will NEVER do any work.
Again, this may not be a "problem", but it's not ideal. Multi-engine boats gain appreciable electrical robustness with the addition of external voltage regulation with something like the Wakespeed WS500 regulators on each alternator.