According to Wookieepedia, Twi'leks and humans can interbreed, although given the popularity of Twi'lek women galaxy-wide and the fact it's not overflowing with such hybrids by now, I'd tend to think the chances of conception were slim. Maybe you would have to be at least a latent Force sensitive, or something?
Anyway, Sith needed their alchemy to breed with humans. I'd think they'd need the alchemy for Twi'leks as well, but no solid evidence comes to mind.
Could Sith and Twi'leks interbreed at all, and if so then what are likely methods?
POSTER EDIT: Sith purebloods being the species (except then after a point they were all human hybrids to a degree, eventually interbreeding themselves to extinction into human populations apparently... So either iteration as long as we're talking red skin, facial tentacles, etc. NOT the dark side Jedi equivalents) Interbreeding meaning offspring were produced. I'm sure an inventive individual could find a way to have a wild night with just about anyone... Or anything... In theory... BUT I SPECIFICALLY ASK CAN THEY MAKE KIDS. bleaches brain breeding in biological terms! I was asking because I was making a Sith/twi'lek/zabrak hybrid OC and then realized I had no idea if that was even possible in strict canon, or in the expanded universe. So, the question was posted Strict Canon or Expanded Universe only!