No they aren't. Sirio engines are designed and manufactured by Star Motor Engineering. There is nothing in common with Nova based engines.
So resuming, you have:

Picco, and some derivative OFNA and Team Orion Wasp engines.

Novarossi, and all its derivatives (Rb, Novamega, Novamax, Mugen, JP, Rex, Top) and countless tuner engines.

Rossi

Sirio, and its derivative Tuned M.Collari version.

AFM