Certainly adcom and faculty expect academics to be your top priority at wharton - especially with the full-time program. As an alternative, Wharton offers an EMBA program for working professionals.
When it comes to working while on the FT program, it is possible IF you
are in control of the amount and timing of the hours you work. If you
are having to respond to the timing of customers or a boss, then it
probably doesn't work as well. But if you are talking about researching
and establishing your own business venture while at school, then that
sounds pretty flexible and something that you could fit around academic
obligations pretty easily.
Wharton's program involves about 15 contact hours per week, and a rough rule of thumb is that you should be spending 2 hours in private and group study for each contact hour, for a total of around 40-50 hours per week. This leaves plenty of time for other activities. Wharton treats its students as adults, capable of making their own decisions about where they place their efforts. I agree with Victor - there is plenty of time, it just depends on what YOUR priorities are.
And adcom and faculty recognize that 'experiential' learning is often jsut as powerful a teacher as the classroom - indeed, someone who isn't pursuing the experiential learning opportunities that abound at Wharton probably isn't getting the most from their MBA experience. And there is a strong argument that the business planning process around a new venture is actually a plus when it comes to academics, as it can make business problems seem more tangible than just dry theories. And most professors are more than willing to spend time with you talking over issues you are facing in your venture that are relevant to their classes/areas of research expertise.
Most students spend 5-20 hours per week on job search activities - if your interests are entrepeneurial rather than traditional employment, then you can spend this time working on your venture, without compromising any other elements of the Wharton 'experience'.