First of all, who else would've killed for Ditto Eggs in the main games.Decided to play a bit of Explorers of Sky and i just got a Ditto from an egg (yes, an egg) received through Spinda Cafe. Is it a good mon to train, or is it too gimmicky?
I never recruited a Ditto myself, but if Transform is the same for your team as with wild Pokemon, it only changes what Ditto looks like. It won't gain the moves of whoever it Transforms into and will be able to use Struggle after using Transform's 1 PP. Believe it or not, that's not as bad as it sounds. Struggle is really powerful in MD2, (Power 30 IIRC when most good moves like Flamethrower, Energy Ball, and Brick Break have Power 12-18) and you don't have to worry about PP, so Struggle makes it slightly tempting. Now that I think about it, I kind of want to see what a team of 4 Pokemon that can only use Struggle can do. I'd say try it in an easy dungeon for a test.
If Ditto does gain their moves, I think the Pokemon it transforms into is random enemy Pokemon that can be found on the floor and they have 4 random Level Up moves, (upto the Level they are, obviously) so Transform would be way too gimmicky even if it had more than 1 PP. A 4 Ditto Team might be fun with a bag full of Max Elixirs though.
TL;DR Either more gimmicky than in the main games or gimmicky for a different reason but strong because of Struggle after using its 1 PP move.