I apologize for the delay in responding to this question...it really belongs on the UEB forum. I thought it was there :(.
See 5.11 of the UEB code on use of grade 1 indicators in grade 1 text. It does mention the question mark used in an unusual position (meaning a grade 1 indicator might be required for the question mark). I think, as the transcriber, you need to decide if there is a chance that question mark could be read as anything else. If there is a possibility it could, use a grade 1 indicator. If not, no grade 1 indicator required. 🙂