RoboHelp HTML projects are reasonably location agnostic. This means that projects are generally able to be zipped and copied to other PCs and used without issue. This alone should tell you there is nothing particularly "machine dependent" or really even "folder dependent" about any of the files.
However, it's worth noting that when you use RoboHelp to add a project to a source control system, it will add all project files except those listed below.
If you are manually adding files to a source control system, you should avoid inclusion of the following files:
Note that ProjectName varies from Project to Project. It is the name you assign to your Project at the time it has been created or when it is specifically renamed.
Certainly Source Control databases are centrally stored on a network. So you are correct in your assumption. It has to be this way in order for two or more users to share equal access.
However, most Source Control systems utilize something called a working folder. This is a folder designated on your local file system. Your C drive typically. When you choose to check out and modify files, they are copied down to your working folder before you make edits.
Therefore, while it would appear that you are working on files stored on a network drive, in reality those files are silently copied from the server to your hard drive before you edit them. When you save and check them back in, they are copied back to the server.
The Troubleshooting Guide has links to the troubleshooting tips for the other RoboHelp forum categories.