I have "inherited" what I believe to be a G5RV antenna with two 51 foot wire centerfed radiators. If I remember correctly from measuring 2 months ago, there is about 31 feet of 450 ohm ladderline which then interfaces with the 52 ohm coax through a sealed choke of some sort. I do not know if it is current balun or voltage balun or whatever. At the far end of the feedline where the coax connects to the transceiver through an antenna tuner, an ohm meter across the coax center conductor and its outter shield shows a virtual short. Am I correct in assuming that that is ok because the choke is essentially one side of a transforrmer coil and I won't hurt the old Yaesu FT901 boat anchor w/ 6146 tube finals upon tune-up?
Yes, it is okay that a DC measurement shows a short. An antenna analyzer would probably be a better test for you.
It's very difficult to say. The DC short or not isn't relevant: it's the impedance at the transmit frequency that's important, which you'd measure with an antenna analyzer or similar.
A DC short may or may not be indicative of a problem. There are some balun designs that look like shorts. There are some that do not. Some matching networks include a shunt inductor which makes a DC short. But there may be no such matching network installed.
If it were my station, I wouldn't make any assumptions. I'd start isolating components until I determined precisely where the short is, and only then make a determination if it's a problem or not.