Since it is generally suspicious practice to disable the isHSQL case,
  A) the scope of the disabling should be minimized
  B) there should be a comment explaining why it's acceptable in the current situation (e.g. "the test case relies on partitioning that HSQL does not recognize" or "VoltDB is correct but HSQL has a bug here documented at: ENG-..."). 

In the current situation, I am supposing that the issue is that HSQL's error message does not match ours, but if that is the only problem, I would allow the test with HSQL and validate that it at least threw some kind of exception but then put "! isHSQL()" guards around the specific error message checks -- let HSQL give whatever it wants to for error messages, so long as it confirms that we are supposed to be raising an error in each case. 
This is a minor issue (marginal improvement) and only effects the test, so, if you prefer, you can go ahead and merge this pull request as soon as jenkins passes.
Then I think the whole change would still be less than 20 story points.