I don't have the option of a doula one way or another; however, my sister had a c-section (not scheduled - baby was breech and came early) and still brought along her doula for support.
I'm going to talk to Dr. about tomorrow. I researched Doulas over weekend, looking for one who was open to all birth options. From some of the reviews I read, some people felt their Doula really pushed for natural and didn't want to dissapoint their doula therefor had a bad experience, this particular one was refered to as overly crunchy in various reviews. I want to have the option for drugs because you just don't know! I think you need to discuss the topic as you interview.
Not sure if by "natural" you mean "drug-free" or "vaginal birth". Either way, you definitely can still use a doula, although I'm not sure how much help they would be in a scheduled c-section scenario. If you're wanting to use meds and go vaginal, you just need to find out as you interview doulas what their philosophy/stance is on this sort of thing. Make sure you pick one that is open to you using drugs, and make sure you're both very clear on what her role is - it's to help you through labor, NOT try to force you to stay drug-free. As long as there's a clear understanding and mutual agreement, I think you'll be ok.
For my first pregnancy our childbirth class teacher was a doula. She seemed like she would be really great in a birth situation whether you want to go natural or not. I think its a good idea. My DH was kind of nervous about the whole situation, so I could see how it would be nice to have an experienced person there to guide you through.
Re: Not doing natural and using a doula?