After the connection is made, they will be at same voltage and freq.
Other factors will determine direction & magnitude of energy flow.

Does this sound loony to anyone else? There is nothing in most
generators to keep the voltages or frequency the same. Well, okay,
sure, once you put the two wires together, yes, there is now only one
voltage in the system, running at some frequency (or, rather, some
combination of fequencies). The question here is: are the voltage and
frequency the one you want (120V, 60HZ), or are they something unusable
(varying voltage, pulsing frequency)?

The important part here is the _phase_. If the frequencies are even
slightly off, you can never get them to stay in phase, resulting in a
pulsing combined signal. Totally useless. If you could get the
frequencies to be perfectly matched, and stay that way (a physical
impossibility*, btw), you would have to then get the phases lined up.
Here you might be able to get away with the light bulb trick, since it
probably wouldn't matter for most devices if you got a perfect match.

* why is it impossible? Same reason that you can never tune a piano
wire to a precise frequency, or even match exactly to a reference
frequency. To get ever more precision, you have to wait ever longer to
hear the beats in the output signal. The only way around this is to use
some kind of active system, like the honda DC generator system. If I
remember correctly, they have electronics in the two inverters talk to
each other continuously, to keep them pretty much in sync. It is not
just a matter of getting in sync then letting go, instead they are
constantly readjusting the outputs to keep them from drifting away from
near synchrony.