the trainer was created originally to work with the single player missions, which were infantry based. The trainer is for infantry mode only. The only option that will work if you are in the flying vehicles is the easy vehicle kills.
They added skirmish mode recently, but the trainer still works 100% for the missions which are infantry and the skirmish Walker Assault.
We wont be creating new trainers to go with each new skirmish mission they create.
The trainer is up to date and working as it always did for infantry based missions.