You should make and option to add it anyway manually if the rom is not in lutris database. Mame games are a hell for example.
Right now if someone wants to add a ROM that is not in the database or is modified, we have to add a recognized rom and edit it, which is impractical and nonsensical.
PS: no, I refuse to use two launchers (lutris+mame nor lutris+retroarch) if I need two launchers something is not being thought well.