What baitcasters are rated for 17lb fluoro? The highest rate I've seen is 14lb.

Reels are rated for lines, so much so as the markings you see on them. Rather, they are guidelines of approximately how much line that reel will hold given the test as mono.

If a reel holds 140 yds of 14# line, it doesn't mean it can't "handle" lighter or heavier line. What it means is that it will hold about 140 yds of 14# test. If you choose to put 17# test, this will mean that it will hold less and if you put 10# test, it will hold more of the same line type.

That is all.  The ratings you see are basic guidelines of the reel's line capacity.

X2

But if you are really looking for a reel that will hold a lot of heavier line here it is:

http://www.***.com/descpageRLCSHIMANO-SHC47.html

Is it the same with spinning reels too?

Yes it is just a recommendation for what size line to use on spinning reels too.  If you want a spinning reel that would hold a lot of 17# test you would need a 4000 series or larger spinning reel.