If your consolidated they will have no issues. Even if your not they will work with you if there are no other options. You will more then likely need a currency sim anyway due to the time you will miss. Delta generally has no problem with mil leave especially if it is a school. Where they get upset is if you drop trips over a holiday to do one paperwork drill or consistently place a drill day right in the middle of each on call block on reserve. A large portion of the management pilots were or are in the reserves. They know exactly what your doing in those cases.
They have had issues with a few individuals who showed up for in doc and then dropped long term orders on them. Still not much they can do about it.