Vinyl REALLY wants a FLAT, LEVEL surface. If these conditions aren't met, 1) you could void your warranty, 2) you'll see 'bumps and waves' in the floor, 3) you'll get cracking and splitting and separation (most likely) too. I'm sure there are more 'problems' that would result but IMO, you're best bet is to remove the ceramic tile and the backer-board. IF you'd like more info, get the Warranty and Installation info from the mfgr. you're looking to install. THAT will tell you what's OK and what's NOT OK in terms of 'backing'.
My best to ya and hope this helps.
Jay J -Moderator
PS: Others will pass by with their opinions, so stay tuned ...