In general, I think there should be a high burden for most folks on whether custom code should be permitted in these cases. I have absolutely seen the same, and this almost always comes after someone makes a reasonable decision to go with COTS, followed by new folks in the role abandoning that rationale for that commitment and companies not knowing how to tell customers "no" or even more importantly "We don't solve that problem, but we're happy to support ways for our system to work with something you procure or build that _does_ solve that problem."