I don't know the details of slab allocators. Though if you are describing an allocator that does not have knowledge of what the memory is being used for (e.g. the difference between asking the allocator for memory for a position component defined as three floats and also a color component also coincidentally defined as three floats, versus asking the allocator for two sets of three floats without regard to their intended usage), then it is not the same.

Some slab allocators are type aware, because some of them reset "freed" items into a type-specific initialised state ready for re-use