This far out from surgery he should be able to take it. There is a correlation of a higher incidence of pouchitis if taken post surgery, in the early days. I take Advil on occasion because like your son, Tylenol and Aleve do nothing for me. As long as he's not using it daily it should be fine.
dx proctitis in 1987
dx UC in 1991, was stable until 1998
1998 started prednisone, asacol, pentasa, nortriptylene, ativan, 6MP, rowasa enemas and suppositories, hydrocortisone enemas, tried the SCD diet, being a vegetarian, omega 3s, flax, pranic healing, yoga, acupuncture, probiotics
2000 lost all my B-12 stores and became anemic
2001 opted for j-pouch surgery- now living life med-free