Can you use Maaser for a Yissachar Zevulun Agreement?
You are asking an important question.
The answer to this depends on how we view the Yissachar Zevuln agreement. According to R’ Moshe Feinstein zt”l (Igros Moshe Y:D 4 37 (4,14,19)) the agreement is more of a business type of agreement, where the two are splitting the support and learning. Therefore, he says that one may not use maaser money for his personal business. Others (The Beis Yosef in Avkas Rochel- 2, Maharam Alashker Teshuva 101, R’ Hai Gaon quoted in above Teshuva) held that the Zevulun gets his schar for his supporting the Yissachar, and causing that he should be able to learn, but it is not possible to buy a person’s reward in olam haba or a business partnership in the torah. R’ Osher Weiss Shlit”a (Minchas Osher-2 siman 58-5) explains that according to this, the way the Yissachar Zevulun works is that when the agreement is made, which causes that now the person is able to learn, because he is the one supporting him and enabling him to be able to learn it is as if the Zevulun is learning together with the Yissachar. Therefore, he is not getting the schar of the Yissachar, rather the schar of his own learning. He therefore says that it is permitted to use maser money for a Yissachar Zevulun agreement.
As a side point see the following post According to R’ Weiss the Yissachar is also not losing out at all by his making the agreement, because each one is getting the reward for his torah learning.
One other point, the Yissachar should not make such a deal if he doesn’t need the money, because it is an embarrassment to his torah, to partner it when it isn’t needed ( Avkas Rochel mentioned above). Secondly, if the partnership isn’t needed then Zevulun is not really causing Yissachar to be able to learn.
Please see the following link https://dinonline.org/2021/08/12/is-there-any-downside-reason-not-to-agree-to-be-a-yissachar-or-zevulun/