Yes, Vixie syntax is supported there too!
See "(mcron) Vixie Syntax".

But if you can grasp the Lisp syntax instead, I'd recommend you for it, it's
much more flexible.  After all, it's the sole raison-d'être of mcron with regard
to cron :)

I think your solution to "every N minute" is correct.

Cheers!
-- 
Pierre Neidhardt