Our ROC was approved a couple weeks before my husband's N400 interview, but since he filed under the 3 year rule, I went with him for the N400 interview, hoping they would let me into the waiting room. No one at security in the lobby even asked why we were there or who we were; we just went through the scanners and on up to the USCIS office. No one in the office asked why I was there either, just told us to have a seat. My husband said the IO asked him like 3 times if I had come with him to the interview, so it was good that I was sitting just outside in the waiting room. The officer even saw me there when he came out to call my husband in for the interview, so who knows why he asked about it so much. It's worth a shot to try to go, even just for moral support, the worst they can say is no and you have to wait outside.