First-
Can you use the same domain name for two services like can you route a game server and web using the same domain name as long as they are on different ports. (I hope that question was clear.)
Second-
Is there a way to safely stress test your servers without affecting the isp or DNS resolver host? Maybe like a local network DOS or something, I don't really know.
Yes you can. I have a domain I bought just to use with NO-IP.org to mask my IP for a Ventrillo server and a Minecraft server. (Each is on a different port) If I made a website using that as well it would work. All about the ports.
Little FYI too - use Port Triggering as opposed to forwarding with whatever you setup. More secure. If you want more details Google it. =)
I already have port forwarding/triggering experience and i use no-ip to its great lol but yeah tahnks for your help.
Anytime man. I love being able to help other community members.