You are limited to 512mb ram per gear I believe on openshifts free tier which is not enough in my opinion to run a stable system plus you are limited to 1gb file space. Plus I have personally not tested ServUO on non debian based Linux distros so cannot personally attest to stability or compatibility.
You would be better off using amazon AWS free tier which allows you to create an EC2 instance with 1gb of ram and 30gb of SSD space. If you go this way I recommend creating a Ubuntu instance.