Your doubts are true. Ace is written in Ruby, while MV is written in Javascript, so it won't work. Unless you know how to make Ace and MV drunk, so they can talk in the same language.
I mean sure, by having MV you can add your very own content into the local version of the game (like orgy, or your own hero), fix certain aspects of the game (like that guard in the royal chamber talking about the board), but you don't really need MV to make all girls pregnant.
Everything you have to do is to use save editor to turn on those switches responsible for pregnancy of every girl. But it might take some time, because there is a lot of them. Just by quick look into database I found around 50 (301 - 320, 361, 362, 381 - 410) switches responsible for pregnancy.
But, as I wrote, you don't need MV. Just upload your save file (and system.json file from game's data folder) into save editor, use ctrl + f, type "pregnancy" and press enter to jump from one pregnancy switch to another. Just don't forget to enable them.
It should be save to turn them on without any problem ingame, because now (as far as I know, but I might be wrong) those switches are responsible only for changing the pictures of hearts in CG's room.
But I'm not taking responsobility for any problems (bugs, errors, game crashes, corrupting save files, turning one certain events, etc.) it might cause. So if it happends, don't blame me. You have been warned.