I would imagine that all audio ROM drum loops in arrangers come with the same copyright restrictions that also apply to their ROM sounds and the ROM styles...

You can use them for musical purposes, but you can’t use them to create competing audio products. In other words, if you copy the samples and then use them to create a competing sampled audio product (say for instance a software drum machine that uses Korg's latest PA5X drum kits and their styles) you are likely infringing copyright.

But if you sample those same kits and styles to create something for your own use ONLY, it likely comes under 'fair use' laws. Mostly it comes down to money..!

The situation might be more flexible with a LONG discontinued product, especially if the company that produced it went belly up. But most of the time if it's sounds from a reasonably recent keyboard (or software ROMpler) I wouldn't recommend sampling it bit for bit and trying to sell those samples or loops.

Sampling synths is a bit of a different case, because you're not duplicating the exact synth engine, just recording one of millions of possible sounds. But copy a workstation's raw ROM for a commercial product, I'd run that past a competent lawyer first!