I'd say there is no absolute "yes you can" or "no you can't" answer. It's going to depend on the two generators and how they are designed to sync.
In fact, even with the honda's, you CANNOT sync ALL honda 2000's with the new honda 2200. there is a serial number break on the 2000 which below if you try to parallel with the 2200 honda says you will get low voltage output and possibly damage BOTH generators.
To be safe, only parallel generators that are spec'd to be paralleled with each other. Or take your chances and as Clint says "Do you feel lucky?"