Crocs do not make your feet sweat any more than they normally would, but because the material that Crocs are made of they do not absorb the sweat that your feet does produce and it can accumulate.
Crocs are made of a material called Croslite that is not porous like leather and other materials that other shoes are made from. The sweat has no where to go in Crocs except accumulate. The holes in the upper of the footwear will allow some of that sweat to evaporate. Wearing socks with Crocs can help absorb a lot of that normal sweat, especially if you are going to run in them.
If this sweat is allowed to accumulate over a longer period of time, there can be a smelly foot problem due to bacterial breakdown of the fatty acids in that sweat. To prevent this you need to practice good foot hygiene and keep your Crocs clean by rinsing them with water and allowing them to dry.