The answer to this is: No, beer won't substitute, but another vinegar could.
The main reason here is flavour - beer tastes completely different to vinegar, and would change the flavour profile of your marinade substantially. This may work out, but it may not, and the only ways to tell would be to test it and/or look for recipes with the same ingredients as your marinade but beer instead of vinegar.
Another reason beer might not work work is that beer is not generally acidic, whereas vinegar has a substantial amount of acid (acetic acid in the case of vinegar from grapes) in it. The acid will help macerate/soften the tissue so that it is easier to eat. Having said that, beer will contain enzymes that break down protein, that might do the equivalent of the acid, but these may not work in the presence of other substances in your marinade recipe.
Interestingly, if you are going to marinade with beer, use a canned pasteurized beer or a fresh brew of unpasteurized beer as the proteolytic enzymes in the beer are broken down in unpasteurized beers (warning: PDF, possible paywall).