Can you lay carpet tiles over outdoor carpet?

It is possible to do but not a recommended practice

Carpet tiles are designed to be installed over a stable surface. Even if you use one of the solvent based outdoor adhesives there will be some movement of one carpet against the other. This abrading will result in premature separation of the layers and you will be constantly trying to re adhere sections of the floor as they come loose.

The best procedure is to remove the existing carpet, prep the surface & then install the tiles.