Go for it :]
Variety is awesome. And so are terriers. They'd make excellent spies (since they're small...er, are more difficult to track because of their wiry fur and stuff, and can hide easily) or small-game hunters (teaching pups how to hunt or trap some of their first kills).
Yesterday, I took a visit to the local dog park. There was a teeny dog in the big dog area, and despite the size difference, she was able to hold her own against the biggest ones. So it is entirely possible for her to survive.