Short answer: Yes. Soil is just as deadly as stone when it comes to cave ins.

Rather than dig the ridge out from under it, go up one z-level and tell your dwarves to channel instead. They'll clear the same area, but as channeling also removes the soil floor tiles, it won't result in any cave-ins. (Though you may need to clear some trees, biome depending)

Short answer: Yes. Soil is just as deadly as stone when it comes to cave ins.

Rather than dig the ridge out from under it, go up one z-level and tell your dwarves to channel instead. They'll clear the same area, but as channeling also removes the soil floor tiles, it won't result in any cave-ins. (Though you may need to clear some trees, biome depending)

A safer alternative is to turn the hill into Upward Ramps (with R or r, I think?) and then remove the ramps with z. A two-step process, but no cave-ins, and no falling dwarves (even 1 z-level falls occasionally cause injuries).