Very good question! Just last week I had the same idea when trying to read the embossed date code in a GE reflector lamp. I think the answer would probably be yes. The glass in those older lamps used to contain about 20% or even 30% lead oxide by weight, which makes it an excellent absorber of X-rays. I think if the accelerating voltage was set to at least 75kV it should be possible to penetrate the glass, and then any thickness variations should show up. When I have a moment I will take a couple of these kind of lamps in to work and have a go on the X-Ray machine.
Nice! If you do go and xray some lamps, do try and post the images here!