Unless it's very easy to set up Selenium on localhost on all platforms (is it?), committers should be able to submit code to run on the test servers. Otherwise, there's no way to tell if your code causes no regressions without committing it -- and code should be tested *before* commit. (As well as an automatic run after commit, since we don't know if people actually did test before committing.) As far as I know, projects with test servers tend to also allow committers to submit code changes to them for testing.
It is not easy to set up Selenium to test all browsers on all platforms. I've been at it for a couple weeks now, and I'm running into a lot of bugs and strange configuration issues.
I'm not opposed to letting committers access the grid. Unfortunately, we may not have the resources to do it with the current system. After we do some initial testing, we should know how much load it can handle, and determine from there whether or not we can support direct access from committers.
Respectfully,
Ryan Lane