1) One may pay a non religious worker or employee, even if it is clear that he/she will not separate Ma’aser from their paycheck, and there is no problem of “Lifnei Iver Lo Siten Michshol- before a blind man do not place a stumbling block”. (Psak of Dayan Yisroel Yaakov Fischer quoted in Sefer Hilchos Ma’aser Kesofim.)
2) One may use Ma’aser money to pay the cover charge for a “Dinner” or a “Melava Malka” or other function which is organized to benefit a Tzedaka organization.
However, the cost of the actual portion should not be paid with Ma’aser. (e.g. if a reservation to the dinner cost $180 and you would pay in a restaurant for a similar portion of food $20, you may pay $160 toward your dinner reservation from Ma’aser money) (Rav Yaakov Kamenetsky Zatzal in Emes L’Yaakov Y”D Siman 249)