[panmanmatt]

They may mate, but may not. Your male is not a kelloggi so if your females definitely is then there is a good possibility that they won't cross breed.

Also I hope you QT'd the new female. The horses you are buying are not true captive specimens but rather they are raised in net pens in the open oceans/bays. From a health stand point you are buying a wild caught seahorse and all the bacteria/pathogens/parasites that come with them. This puts your existing horse at a huge risk, especially if they are of different species.