Absolutely yes, concrete slab is a suitable and one of the commonly used materials for the pizza oven foundation and you can use it. It has several features that make it one of the most preferred materials e.g. it is firm, it doesn’t wet therefore the oven remains dry especially for those in outdoor setting, and it is durable.
However, if you are planning to use a concrete slab for your pizza oven, then you must be able to bear the costs burden. The concrete slab is expensive compared to the possible alternatives e.g. sand slab or clay slab.
Further information: Make your own barrel brick pizza oven and outdoor setting, How to build a pizza oven, and Build a wood burning clay pizza oven