Why not ask your corporate travel and the corporate TA? I have to presume that UA marketed this to its corporate customers and their TA's as a cost-free (to the employer) benefit of UA. As jsloan notes, I can't imagine that a rate explicitly noted as "leisure" can't be used for leisure.
If it's a better rate (with the exact same fare rules) as your business discount, no reason not to take advantage of it for business as well, although I would be surprised if there isn't something in the fare rules which makes the business travel bucket "better".