Freshwater bacteria on Saltwater

[Johnny Reefer]

I would say no.
Saltwater systems have other bacteria involved, besides Nitrosomonas and Nitrobacter.
Namely Nitrosococcus mobilis, N. oceanus, and Nitrospira spp.
I would think that if you started off with a seeded FW filter, you would have an imbalance of too much of the Nitrosomonas and Nitrobacter and not enough of the others.
I think it is better to start from scratch and let the filter balance itself out right from the get go, IMHO. (If that makes any sense?)

Cheers,