simcha613
There are some kollelim that work like that but they are set up different. I believe there is a special yissachar zevulun contract for people who do that. Its also more one on one, meaning, a gvir will make a contract with a certain yungerman commiting himself to a certain amount of money a month in return for his limud hatorah.
Most kollelim though are more general ie. the rosh kollel either has a main mefarnes who keeps up the kollel or/and goes around collecting for his kollel (usually they know a few gvirim that they collect by, I think). In this way there is no contract or any form of business deal between the two individual parties.
Real Yissachar Zevulun deals I think are pretty rare.