Easy enough:
http://www.ppfahome.org/abs/faqabs.html
Quote:
Can ABS pipe and PVC pipe and fittings be used within the same system?
It's not recommended. However, ABS pipe and PVC pipe and fittings can be joined when connecting building drain to building sewer materials, if you use proper transition cement and adapters or other methods as approved by local plumbing codes.
Note the only specs that are recommended for abs piping are for DWV systems. That is Drain Waste and Ventilation. Not pressure as a spa requires.
Besides, PVC pipe (as well as flex) is so cheap I can't see any reason why anybody would ever want to mess with anything else.
All the fittings in this industry are made from PVC, so you'd definitely encounter additional problems joining them to ABS.