Yep, the rats do still burrow underneath, but as you said they are even burrowing under your concrete base, so it won't make much difference.
And if its Rebecca Torrance you are thinking of with the rats burrowing under the slabs, then the reason she put down paving slabs was because of the rats burrowing in the first place when she just had an earth floor.....
I would recommend concrete first, but paving slabs next.
Beth