I have had a tooth abscess for sometime now. I have developed a real bad skin rash. Can this be related?

Depends. If the rash is immediately adjacent to the abscess it could be related but not necessarily. Delaying treatment on a dental abscess is never a good idea so please get it looked at ASAP.
Possibly. An abscess is a virulent infection. Abscesses do not self-cure. As they spread they can cause damage to other organ systems. Please seek emergency dental treatment now.