Dropracks are suitable for use with a roof tent, but your roof tent will need to use 20mm t-bolt fittings to attach to Dropracks. U-bolts or claw type fittings are not compatible with Dropracks. You'll also need to check that the feet and fitting kit you are using are OK to take the weight of the tent plus Dropracks.
You'll need to use the roof tent at roof level, not at the lowered level. The frame is not designed to support the weight of the tent plus the occupants when it is lowered. It's fine to install the tent whilst lowered, you'll almost certainly find this easier and quicker than installing it at roof height.
It's fine to attach the tent about the cranking aerial, if you need to. You can still wind the Dropracks up and down using 180 degrees of motion in the crack handle.