Can a virophage potentially be used to cure a viral disease?
There are few enough virophages occurring in nature that I don't know if there's a clear and compelling case for them being potentially therapeutic.

In principle however, the answer is yes, though they may suffer from the same problems that bacteriophage treatments have suffered during their history - difficulty in preparation, extreme species specificity, and fairly daunting regulatory hurdles. While viral diseases don't have the "Or we could just use antibiotics, which work" out which made bacteriophages less popular, as far as I know there's not been a suggestion of widespread virophages against human pathogens.