Licensing (in your case) demystified:
Windows Server 2003 Standard - One License
Windows Server 2003 Enterprise - 1 host + 4 VMs, all using the same license. (Only allowed to use the host as a host for VMs, and can’t run anything else on it… Or you can use 1 host + 3 VMs, and can use the host for whatever you want.)
So, if you have an Enterprise license, I’d definitely go with VMs for Ignition. If it’s standard, you’re probably stuck with the one install.