Um, adding dependency to yast2-storage is bad IMHO, it has too many dependencies (yast2-storage -> libstorage -> [cryptsetup, device-mapper, diffutils, dmraid, lsscsi, lvm2, mdadm, multipath-tools, parted, udev] -> <other dependencies>). This would increase the needed space in small appliances.

IMHO it would be better have it optional (as Recommends: dependency if it makes sense to have it installed by default or Suggests if the dependency is really weak (not installed by default)). And the use a wrapper for calling Storage.

You can check yast2-packager, there is a storage wrapper:
https://github.com/yast/yast-packager/blob/master/src/clients/wrapper_storage.ycp

The wrapper is called this way: WFM::call("wrapper_storage", ["GetTargetMap"]), this returns Storage::GetTargetMap() result or nil when the Storage module is not present.

See https://github.com/yast/yast-packager/blob/master/src/modules/SpaceCalculation.ycp#L565

You can reuse the wrapper from yast2-packager directly as it is already in yast2-country Requires, so no new dependency.