The ground crew guys are probably wearing haznat suits becasue the X-37's orbital maneuvering propulsion system uses hypergolic propellants which are quite toxic. The purpose of some of the tubes connected to the spacecraft are to purge and absorb any residual hypergolic stuff
It's actually to protect against the Chemical dispersants that are still active on the vehicle after re-entry. The Chemtrails don't show up because of the altitude of the orbit.