I was surprised to hear a lecturer pronounce the word עם in the phrase עם הדומה לחמור with a חיריק. I know that all of my teachers pronounced it with a פתח. When I pointed out the גמרא at the end of כתובות (111a), which uses the דרש to connect slaves to the word עם with a פתח, he sent me to the מהרש"א, but I'm not sure which way it points.
Can someone show a clear source which discusses this question, or which clearly proves the answer to be one way or another?