I don't think there is a limit, but I seems to recall a mention in the Administrator PDF, saying that you shouldn't have more thsn 20 SEPM server linked together, so something to consider.
But if you're only using the domains on a single server, it shouldn't be a problem however hardware requiremnets might need to be a bit higher (more memory & better CPU) in order to handle the databases & flow of data from each domain/ADs.