I installed nginx instead of Apache and had a slew of problems with it. It seems like Virtualmin doesn't yet completely support nginx.
I wanted to add the rewrites for accessing Virtualmin from each server domain by accessing: http://admin.domain.com but then I noticed that there was some problem with nginx listening to my site specifically. Maybe the sites-enabled was not configured?
It just gave me the impression that it's really not ready for production in a Virtualmin environment.
I hope it will be improved because nginx is really good with high-traffic websites.
Thanks!