I dont think that him being the closer wont be too bad because he's was a great pitcher and he has potential to become a great pitcher again. His Splits show that in his first 30 pitches, he is solid. In 1090 AB's, hes only given up 111 runs which is about 1 run per 10 ABs, which comes out to be about an 3.50 ERA, which is decent for a closer. Dont forget that he has to pace himself when he starts, so when he closes he will be throwing all out.
I dont think he will be the best, but i think he'll do okay if he is given the job