What is the possibility of being rejected by Graduate school if a professor has already acclaimed to give me a RA offer I have passed several loops of evaluation by a professor, who would like to be my future advisor. He told me that he made his final decision on me and was pleased to offer me a RA position in his lab. He asked me to submit my application and he could expedite the application so that I could get the admission quickly. But I have a weakness of undergraduate GPA(3.01/4, he didnt ask for any transcript information during our connection). I'm waiting for the admission information but very uptight about the result. I'm super worried about being rejected by the graduate school because of my undergraduate gpa.
If the Graduate School has the final say, then you will have to wait for their decision - we cannot guess their response, and probably neither can the professor.

However, if the professor has the final say and the Grad School just processes his acceptance then you should be fine, assuming there are no hidden things...