This is fine so long as you have a separate IP address for each subdomain
I've got a number of apps running with Digital Ocean and Forge. They all have at least one subdomain running off the same server typically:
staging.mydomain.com
www.mydomain.com
One has 4 subdomains - all with separate databases. You just need to set each one to have a separate DNS A Record. Doing it via Digital Ocean and Forge makes it very easy as you get a separate IP address for each site.