I'm pretty sure that there is a very LOW risk of impaction with Dubia's. They have less chitin than crickets, mealworms and superworms. I've heard that Dubi Deli is a reliable source, they're just kind of expensive, maybe I'm just used to expo prices. Dubi Deli | Dubia Roaches I believe it is. Here is an add on faunaclassifieds that seems to have a better deal, I don't know how reliable they are though since I've never personally ordered from them, nor have I heard of them. Special 10% OFF Dubia Roaches Size 1/2" and Under Free Shipping - FaunaClassifieds Those are probably the size you'd want, too. 1/2" and under.

I second what Graham said, I don't cut my worms up anymore unless the frog is real small. You could always see if he gets a hold on a hole worm and if he seems to have trouble with it you can always pinch off the rest of the worm. I don't think it'll have trouble though.. as Maharg said, these things are built to consume.

EDIT: Yes, You can use the bowl trick with these roaches. They cannot climb real smooth plastic.