Can I use an antiandrogen for treating oily skin?

Yes with supervision. The use of spironolactone as an anti androgen for acne is quite common and should be used under supervision of a dermatologist.
May Help. Spironolactone may help some, but will not solve an oily skin problem. The best product is low dose Isotretinoin (accutane). You don't want to take this drug is you are at any risk of getting pregnant because it has a high risk of causing birth defects.