Use of a grinder is allowable in a welder performance qualification test in accordance with AWS D1.1.
On a root, feathering a termination, on a tack, or on a cover pass.
If the D1 committee wanted grinders prohibited or limited you would see it in the text. (as it is in the Bridge Code)
You are not the first to ask this question... There is an official D1.1 interpretation on your question.https://s3.amazonaws.com/tech-www.aws.org/interps/d1-86-010.pdf
With that out of the way... The code requirements are a minimum; meaning that users may set forth more stringent criteria for performance qualification so long as the minimum requirements are met.
As an ATF you should be providing detailed work instructions and welding procedures to the welders taking the test. Those procedures should be discussed, vetted and agreed upon by your customers prior to contracting with them.
If your customer does not want grinders used during performance testing, they should make that known up front. Then it is your job as the ATF test administrator to provide clear work instructions and examination criteria to the test taker prior to giving them the test assembly.
However if you exceed the code criteria in any way without making that fact clear, in writing, to your customers and to the welders taking the tests, that may open the door to problems, arguments and possibly litigation that basic process control at your ATF would eliminate.
The blunt reality in this case is that the ATF is unaware of the requirements and it's processes are out of control. They welders are not so sloppy as the ATF is.
As an ATF it is important for you to keep in mind the scope of the users of AWS codes, especially D1.1. It is enormous!!!!! So many users in so many industries, some with the highest level of criteria needs and some very basic job shops and manufacturers. When I began to grasp this, it was a little more easy to understand why things like grinders and undercut are allowable on test assemblies.
Don't take this personally.... Your ATF organization bears the responsibility to provide you with guidance on how to administer and evaluate test assemblies.