I would email and ask, so that you have the response in writing. I also find that many schools are very hard core about their letter requirements, since I asked quite a few schools if engineering could count as a science letter, and most of them would not budge on it having to be strictly BCP. Also, I see that Columbia allows you to submit letters directly to them if your 4 AADSAS letters are already used up, so I would not be surprised if they respond by saying you have less of an excuse to deviate from their requirement.