I still wouldn't install OTA even if you're planning on rooting but not flashing a custom ROM as it could still potentially cause issues if the update ever changes your HBOOT version, recovery, radio or anything like that. Personally, i think that if you're going to go through the rooting process then you're missing out on the best bit by not flashing a custom ROM.
You'll get updates much earlier and more frequently than you would with OTA updates and the long-term development custom ROMs are significantly better than the HTC stock ones.