Yep, the owner of MRC is in a bit of trouble right now. They are a local company here so our reef club is going nuts over it.
Regardless, Andy is only one of the owners... I know there is one, possibly two other owners. They are still selling, still operating. I know many people have a huge ethical issue with giving money to the company given what's happened. I'll say in advance that as reprehensible as what this person is accused of, he has not been proven guilty yet. Of course this is a moot point if you already have the skimmer.
Anyhow, back to the topic at hand...
The valve allows you to adjust the water level inside the box. No matter what, if the skimmer is sitting in the sump, in water, there is no way that the water level in the skimmer can be lower than the water level of the water outside the skimmer. Depending on what level you require, and how deep the water in the sump is, this may or may not be a problem.
I have an Aquatecture skimmer that is pretty similar to the MRC. I placed mine on a little acrylic stand so it sits high in the water, just so that it would never become an issue. A couple hunks of 3" PVC pipe will work just the same. It's cheap and it adds that level of flexibility. I'd do it.