Most 5 strings have 18mm spacing. I've never seen a bass that had a wider spacing than 19mm, so I don't see how spacing would be an issue. And although, I've only heard a few guys do it, there's no reason to slap a B string. It's there to use for other things depending on the kind of music you play.String spacing I find tighter on a five string so it's not just the slap but also the pop you need to be more accurate with. I find the 4 string easier to slap and there's nothing I've learnt to play that asks me to slap a low B string..... well not yet.
But muting the B string can be a problem so it's something you have to be conscious of and work on.