There are a few MSC's with this policy. It's heartless, unfair and NOT an industry standard. I recommend that no shopper take an assignment where they are forced to either put out money on their own or subject an employee who relies on tips to not receiving one.
Not sure if it was SoS, but a few years back a took a table service assignment for an MSC and was declined the tip reimbursement, even though it was within the reimbursement limits.
I argued my point and explained that the policy of not covering tips was not mentioned in the assignment instructions. They paid me the $6 they owed me and changed the instructions to say that tips were not covered.
I no longer work with companies that have that policy, but my point is that you should push back if the tipping policy was not clearly covered and you do not plan on taking assignments with them in the future.