I have a Radio Shack ConcertMade 1500 . It is, AFAIK, a rebranded Casio CTK-650 . I has a GM bank and uses PCM samples (from what I recall of the service manual, it has a 2MB ROM size, AFAICR, no idea about compression used if any) . I seem to recall it not carrying the official GM mark and, AFAICR, there was a rather trivial reason for that, but I do not remember specifically what that reason was .

Anyway, it sounds quite decent, IMHO, as a MIDI output device for gaming . See https://www.soundonsound.com/reviews/casio-ctk-650 for a non gaming review.

AFAIU, the problem with using a MIDI accessible FM synth keyboard to play back computer based music meant for OPL2/OPL3 is that, even if the FM synth keyboard allows control over the way voices are generated and various other parameter, that does not directly translate to the way software with direct hardware access to OPL registers works .

I am not an expert on this, so I may be misguided, but I believe the aforementioned makes playing music from OPL2/3 supporting games on MIDI only accessible FM synths with any degree of accuracy challenging, if not outright practically impossible .

Someone will surely come by and correct me if I am wrong .

I think like darry above, the OPL chip driver have quite other capabilities, then what the game midi encapsulate, and you would have to use a midi driver to communicate with the keyboard and pass them as midimessages.

Any keyboard with the General MIDI logo and MIDI in (or a serial computer interface + the adequate driver) will work for playing back General MIDI.

However, in the case of the Yamaha FM keyboards with MIDI in that won't work, as their MIDI implementation indeed usually does not match with whatever is required for FM MIDI playback, despite their FM chips sometimes being the same as those used in PC sound cards. Also, MIDI ≠ OPL2/3 commands.
That is excluding the FB-01, of course, which will work with any game compatible with that module. You could try a Korg 707, it is based around the same chip as the FB-01, but I have no idea whether the MIDI implementation is the same as on the FB-01. There are various Yamaha 4-operator keyboards based on the TX-81Z, TQ-5, and a few other 4-operator modules, but those are not FB-01-compatible, AFAIK.

I guess it should be possible to build some kind of interface that sends the OPL signal to an external port, and then directly to the chip in a Yamaha FM keyboard, but you'll have to break out the soldering iron...