The short answer is yes, but I suspect you would like more information than that. Well I personally would not advise it, and would not have it in my own home, but I know people that have had it done without any issues at all.
Roman blinds are not moisture resistant blinds. They are made from a soft fabric the same as curtains and pillow cases, and would you put curtains or pillow cases in your bathroom? This is why some companies will offer to make curtains and pillow cases in the same fabric as your romans, looks great all matched up.
Take a look at the video below for more information about how Roman blinds are made, which explains why they are not suitable for bathrooms:
The reason these fabrics cannot be used is they are not waterproof. They will probably be fine at first, but after a while it is likely you will see mould growing on the fabrics. With rollers and verticals this can be fixed with a Teflon coating, but this would not work on a roman blind.
The reason they are so likely to get mould on them is because of the moisture levels found in a bathroom, mostly off of Showers. This reacts with the soft fabric and after a while can start to cause moulding.
This is good news for those of you that don’t have showers though, there is no reason not to have roman blinds. Unless you have a steam room or something similar, then the same thing will apply.
If you’re a bath person though, you should be perfectly fine with a roman blind. Unfortunately, I am not, which left me deciding to choose Shutters. In my house everyone uses the shower, which I believe is fairly standard these days.
To clarify for anyone that has an extractor fan, that really isn’t enough to stop the heat and moisture damaging the blinds. This is just my advice though, you are welcome to try Romans for yourself or get advice from your local advisors.
Just because Romans aren’t suitable for bathrooms, does not mean other blinds are not. The bathroom blinds guide by Harrietts is a wonderful explanation of the different blinds available in your bathroom with an great gallery for each type.