Rinoa is NOT a SeeD . It is mentioned in the game directly , when they waited to see Martin she said something like " Just pretend that I'm a SeeD too ". And beside if she was a SeeD she never needed to hire SeeDs for Forest Owls.
And Irvine is not a SeeD either ,he was never in Balamb garden before and all students need to take their field SeeD test in Balamb garden . and when facing Edea in the end of disk two Seifer says something like "what are you doing here, you are not a SeeD "
So Rinoa and Irvin aren't SeeDs.