Is it possible to maintain a web site or blog site using two CMS?
It is possible, but I would recommend thinking about it twice as you will have 2x the code needed to manage in the future, you could need to do changes in the 2 CMS. Also it means 2x more CMS update, etc. If there is no other way, you can do it, but make sure it would not be possible with only 1 (possibly with plugins?).