Is it Profitable to run a GMOD Server?

Very few servers make money off of their userbase. Just in general it's not likely that your server will make any money, and most of the time it will end up being a waste. Unless you have thousands of members a day and use things like donator ranks, its not beneficial.

It's like forums. Most forums cost much more to run than they actually make, unless you have new members constantly joining buying and looking at ads.

But I feel like running both cus of money isn't a good idea. I don't think your intention should be about making a ton of money if you try to run communities like this. You should actually try to build a community of people you like, rather than try and shill out for them