Yes,, you can run eValid as a service and doing this makes running tests very easy.
IN fact, this is a common mode of use for users who are supporting monitoring function. As a service you simply feed the eValid script, the *evs.file, into the service and capture the output.
In fact, this type of use has been around for a long time. See this page: http://www.e-valid.com/Products/Documentation.9/Monitoring/nt.service.html
Here is a writep that shows how this is done on NT/2000 versions of windows and the same procedures should work on more recent versions of windows.
eValid Monitoring Team