In general,Is there any concern with using the studs (or bolts) on the oil sump assembly for attaching cushion clamp or tabs. Looks like a good way to secure my starter cable
Very commonly done - I’ve never heard of (or seen) any problems. Just keep the “stack” all metal - standard ADEL clamps fit the bill, don’t use all-nylon (for instance).
Anytime you break torque on a piece of hardware that is a containment for liquid (like this) you run the risk of compromising the seal. However, like Paul said, everyone does it bc we don’t really have any other choice. Follow the good practices mentioned already and others that will follow, and only do one at a time and you should be fine.