That's a good question, and I'm not sure what the correct answer is. Theoretically, one would expect dutasteride to be able to reduce sebum; but considering how even the standard approved dose of 1 Avodart per day only inhibits the type 1 enzyme by around 50% or so at steady-state (maybe a little more than that), it may not be all that good at doing it. That's because sebum production in men is apparently already "maxed-out", so you might have to reduce the DHT in sebaceous glands even more than what Avodart is capable of doing, just to get a noticeable effect.
Or maybe it's just that nobody has bothered to test it for that, which doesn't seem all that implausible to me. As we all know, dutasteride is a very powerful drug, and I can see that most doctors would hesitate to have to give it to test-subjects for three months or longer just to get blood-levels up high enough to where it _might_ be able to reduce sebum noticeably.