It'll be a right pain in the proverbial - the needles will drop all over the gravel, and you won't easily be able to remove them. They'll rot down in the gravel, providing a medium for weeds to root into, so no, I don't think it's a great idea - but you know that already, don't you, you already worked that one out, lol!
If you really want shot of the paving slabs, just leave bare soil exposed - that way, the needles can sit and rot to their heart's content. the only drawback might be that, if the slabs have been present a long time, the tree may have roots directly beneath them, which will then be exposed and dry out readily if you take the slabs away.