Gabapentin and Pregabalin supposedly pass through your body unchanged. So since it doesn't put your liver to work, there's probably no conflict between the two there. I'm not sure what the effect on the kidneys might be, but it's likely that if you have a healthy elimination rate, it's probably not bad.
The thing that's more likely to affect you then, is a possible potentiation they would likely have when combined. Increased discoordination, dizziness, generally increased 'highness' most likely.
The safety of this combo is completely unknown, has never been studied and isn't often talked about anecdotally. So don't take my words as gospel. However, in theory, it must be quite a bit safer than combining kava with other meds that metabolize in your liver using CYP450.