I’m on the latest nightly build (2018-05-11) on a Raspberry pi 3 b+ and SCUMMVM works (after following the guide at https://github.com/RobLoach/libretro-database-scummvm, just the usage part).
The only problem I’m having, and I’m not even sure if it is a bug or just a feature not yet implemented, is that no icon is showing up: I have just a black square where the logo of SCUMMVM shoud be and the same thing in the games list. Funny thing is when I go in the information of the game itself (ex. The Secret of Monkey Island) I have all the art and the information.
UPDATE SOLVED
It wasn’t a problem of retroarch/lakka but of the icon pack (Flat UI) that doesn’t have icons for SCUMMVM, changing it to default (monochrome) fixed it.