"Ruaraidh" is rejected as an incorrect spelling, but it is in fact used; it can be found in Am Faclair Beag:
Ruaraidh /Ruərɪ/ fir. neo-ath. Roderick, Rory
I think "Roddy" and perhaps "Rory" are shortenings of Roderick, where "Rudy" is most commonly a shortening of Rudolph (which i haven't encountered here, yet)