Yes most times puppies do swallow their baby teeth when they fall out.
It's very harmless for a puppy or dog to swallow their baby teeth although some puppies may not swallow the baby teeth and sometimes a puppy will allow the baby teeth to fall out of their mouth to the floor.
So you might find a puppies baby teeth on the floor when they fall out or find them somewhere else but most times most puppies will harmlessly swallow their baby teeth.
Puppies when they grow their teeth will have 28 deciduous teeth and then after those deciduous teeth fall out or they swallow them then they will have 48 permanent dog teeth once they grow in.