Tester showing ground, but I am not seeing a ground
Have confidence in that.  Metallic conduit is a higher standard, used in most commercial installations.  Ground is the conduit itself - you don't see many green or bare wires in conduit work. 

However - the outlet screws as the only ground path is not OK.  Pigtail a ground wire from the junction box. Most boxes have have one hole tapped 10-32, for a ground screw... here are fancy ones. Do not use 10-24 or a sheet metal screw!

To keep a bare wire from hitting the side screws (even if you use stabs), wrap the outlet with tape. 

Also go downstairs and make sure the ground path is solid - i.e. all the conduit splices are tightened.  If something makes you nervous, you can double it by running a ground wire, that's the beauty of conduit, you just can!