Even a 2.5 inch dwarf frog could stuff guppy fry in it's mouth. Their water parameters (temp, cleanliness, pH) are quite like those of guppies. They in turn can be harrassed by many of the same tropical fishes which might bother your guppies.

If yours are the 5 inch long African clawed frog, you may want to get them out ofthe tank soon. You may still decide to raise the dwarf frog separately from the guppies. At least watch them to see hoe they react to baby guppies.

On the other hand, most guppy people actually have too many fry around the house. If you have a tank of fry, that may be all you will need.

Interestingly enough, dwarf African frog are also  vulnerable to Camallanus, a scorge of guppies. Both the frogs and guppies could be treated with a dewormer as a preventative treatment, if you so desired.

The problems with Camallanus include the fact that they are seldom detectable in a 1-2 week quarantine. Also, by the time the Camallanus is discovered, the adult fish could be in pretty bad shape.

Keep their tank well covered. Just because they are aquatic doesn't mean that they aren't a little adventuresome. ;)

All the best,
u.s.

Here is an article on how to tell them apart.