Good questions BigFoot. The SWR is a measurement of antenna matching, not the transmitter. True that a high SWR can damage a transmitter but at these power levels I doubt it would do damage to the RC unit. I work with 2.4 ghz units designed to attach to a dish, vertical or panel antenna and I do testing most of the time with any antenna or other load attached to the transmitter. I have not had one unit be damaged by this yet. The added reflector should not change the antenna impedance or SWR provided it is mounted at the focal point of the reflector. A good way to check it is to use a laser pointer and direct the beam straight into the reflector surface at several different points and the beam should be seen on the antenna in all cases. If it is not aligned properly the beam will not shine back to the antenna and thus won't work properly.
I received my set of Skyreat Aluminum Parabolic reflectors in today from Amazon. To test them, I flew the Phantom 4 out to 1850 feet at 145 feet altitude, I think, and had a 100% signal reading. I then turned the array to the left and at about 30 degrees, the signal started to drop. At 90 degrees, it dropped to 80% and at 180 degrees it was 68%. Thus when pointed away from the drone, the signal dropped that much! I repeated the test to be sure and got almost the same figures. They do work! But do the laser test and be sure the parabolic surface is free of dents or wrinkles and adjust the array so it can be pointed at the drone.
Good luck,
Jim
WA5TEF