On the remote machine if your version of Firefox happens to be 64-bit it is installed in "C:\Program Files\Mozilla Firefox" folder, so in order for DevTest to find it, it needs to be in the %PATH%. If it was 32-bit, it would be installed in the "C:\Program Files (x86)\Mozilla Firefox".
Update the PATH System Environment variable to have the folder of where your IE and Chrome drivers are on the remote machine in the PATH. Have them match the same location a defined in the Project config file. C:\Projects\Drivers.
Selenium requires interactivity with the desktop, so the only way you can run your Selenium test against a Simulator Service is to run it headless (browser runs in the background and will not interact with user).
On the Simulator Service, update the Properties, chose the Log On tab, Check the "Allow the service to interact with desktop" box, but to do this you will need to use a Local System as Logon. Restart the Simulator Service.
This will allowed to run your Selenium test against the remote Simulator service.
If DevTest 9.1.0 and earlier you can view the screen shots from the Reporting Dashboard.
If DevTest 9.5.1 and later you can view the screen shots in the Portal under the Monitor Test section.