Yes, they are pretty anatomically incredible creatures. And yes, the seminal vessicles essentially replace the ovaries in males.
During mating, the female deposits up to 1000 eggs into the male's pouch, literally within 1-2 seconds of copulation. The male then does a little "dance" to situate the eggs in the copious folds of flesh inside the pouch, during which process he is inseminating them. He then carries the eggs to gestation (usually 18-24 days depending on species and water temp), and gives birth to the fry. It is the only true male pregnancy in the animal kingdom!
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