I think it's common at first. But if the alcoholic truly recovers, entering a spiritual program to deal with their alcoholism, and continues their program, maintaining their sobriety, I think the worry of this fades over time.
My own wife met me after I'd been sober for three years. She worried about my alcoholism a lot at first - I was open with her about it. Over time, she worried less and less about it. After a few years, she never even thought about it. For what it's worth, I've been sober for 24 years now.
I think that was one of the things that made her so certain I'd transition, even though I didn't want to believe it myself. She'd seen things that I'd overcome in my past, and when I told her "My gender issues are beyond my ability to stop - I can not suppress them anymore, I must follow this through, where ever it leads, and what ever the cost, or I will surely die," she knew that whatever it was that I faced, it was serious, earnestly serious. She also knew that I'd never put anything before our relationship - until the moment I said "where ever it leads, and what ever the cost."
My gender has been the most overwhelming and powerful thing I've ever faced in my lifetime. I thought that I understood the concept of "powerlessness" after 23 years of sobriety. After all, I knew that I was powerless over alcohol - if I took a drink, I'd soon be completely out of control. But what I experienced made me realize that I didn't understand powerlessness at all.
My poor wife was right, and I was an arrogant fool.