Yes, it's fine. I've been using both my SYN-2 and SYN-1 with external power switches for about a year.
The only thing to consider using power switches to turn on/off a few pieces of gear at the same time is you might get pops/noise when you turn on off. The SYN-1 and 2 take a couple seconds to 'heat up', so it's never been an issue for me.