Garbonzo beans, no.  Butternut squash, yes. But keep a couple of things in mind.  Squash is a fruit not a vegetable.  I wouldn't recommend eating the squash on the same day as a baked potato.  Not much of a diet considering the carbs involved. 

And watch what you put on the squash.  Don't know anything about the dip you were talking about.  I tend to eat the squash on day 3 just because of the uncertainty around it. 

Keep in mind that you lose weight on this diet like any other and that is burning off more calories than you consume.  You do it right, you can incorporate the squash.  It is wonderful.