I tested the ResidualVM installation in RetroPie a little further today with disappointing results. I copied over several save game files to test at different points throughout the game. ResidualVM will compile just fine and Grim Fandango will load. The intro is very choppy, and the beginning of the game is playable, but there are many more graphically demanding portions of the game later on, and it is definitely unplayable at those points and even crashed my pi a couple times. I tried forcing a lower resolution and tested out different memory splits to no avail.
At this point, I would consider ResidualVM games unplayable on the Raspberry Pi until better optimizations are made upstream.