Since rubber is an insulator if anything it will get "more" hot. I wouldnt recommend covering the entire base in rubber but if theyre small and isolated in the corners I cant see them making much difference.
Edit - I suppose if the rubber feet raised the base off the surface it would allow air to flow underneath, but again I would say it would make little difference.
A lot of (poorly designed) laptops have air intakes on the bottom and outputs on the sides or backs. For these, higher rubber feet help keep it cool. MacBooks have intakes/outputs on the back, no feet necessary.