Except, it won't "goof up" anything. The whole point of the synchronization system is to protect the generator. When it sees something goofy going on, it disconnects itself by tripping the overload.
There is proof that the Honda will sync up to any 120VAC power source. Google it. It'll work with mains power, inverter output, and other brands/sizes of generator. If the power it senses is something it can match, it will.
I have no doubt a honda and a yamaha will work together, but at worst, one or both of them will simply trip their overload protection. Disconnect, shut down, and restart them separately, and all will be fine.
BTW, there are no "signal cables." The bullet connector cables are POWER CABLES. The bullet cables are hot and neutral, so make sure you match them between the two generators.
