Pitfalls of creating a foreign key constraint on a system table?
I did not find an elegant way to solve this question but adding a check constraint on the "Owner" column of the metadata tables accomplished the objective of ensuring that only schema owners would be listed.  If a new schema owner is added then all the check constraints would have to be changed but that is not too onerous.

I tip my hat to Phil for confirming that backing away slowly from system tables is the best approach and wish he had posted this as an answer.