I agree with Op 28/18, I went on my own volition to a derma doc, and she prescribed me about 5 total products, Tazorac cream, Benzawash, benzacream, Vitamin C pads, Glywash, and also oral Dicyclomine (an antibiotic that focuses on attacking dermatological bacteria)...my GI and her both said it would be fine with Crohns to do these things, and I have Severe Crohns Colitis....
I was on Minocycline 2 years ago for acne, because I've had it bad most of my life, but mainly ever since I started working out, and mine's due to high hormone levels (testosterone, naturally attained levels from intense lifting), and that was before I was diagnosed with Crohns or saw much of any symptoms (other than a very mild 6 day flare from early 2006 that went away on its own without treatment, again prior to Dx)...I don't trust the Minocycline, it's more potent and more "total body" in it's methods and range.
My acne was there prior to pred, way worse during pred, and tapered very well once I started treatment for the acne (see my first paragraph above), but I also stopped the pred about 2 weeks after beginning the acne Rx's and creams etc.... My worst side as far as skin (other than subcutaneous water retention, ie: Moon face) was Milia, which is NOT acne, but looks kinda like it, I did a thread on that. Those went away on their own, slowly, but I still have a little left on my chest, which got the worst of the acne.
Id say see a derma doc and make sure Crohns takes a front seat in the chosen treatment for acne.
edit: my derma doc wants to give me a go for Acutane and I was hesitant immediately, but she said she won't give it to me until I get an okay from my GI, my brother was on Acutane for a bit and he thinks it gave him IBS, whether or not that's true, the fact remains that it gave him suspicions of it giving him IBS, and if it made him think he's got that (right or wrong), then I sure as hell won't go on it. I read the entire packet she gave me on it, and the risks included blindness, deafness, heart issues, neural issues, psychotic issues, the stuff is about as toxic as the damn pred itself, and my acne products are working okay so far, but there's still progress to go.