@JonnyC616 - "Riding" override

A "FallingSand" entity is spawned as the host instead of the rabbit, meaning the game looks for spawning rules for "FallingSand". Since there are no rules, it will spawn no matter what the environment is. The "FallingSand" entity disappears instantly because its "Time" value defaults to 0. Other entities can be used instead of "FallingSand", of course. The "Pos" tag must be with the host.

/setblock -247 32 -22 minecraft:mob_spawner 0 replace {SpawnData:{id:"FallingSand",Pos:[-247.5,37.0,-22.5],Riding:{id:"Rabbit",RabbitType:99}},SpawnCount:1,SpawnRange:100,RequiredPlayerRange:100,Delay:5,MinSpawnDelay:100,MaxSpawnDelay:100,MaxNearbyEntities:8}