I've never built anything GPIB related but I've worked-on and worked-with some GBIB boards...
I am seeking some guidance on whether or not it is feasible to use an Arduino to control an instrument via GPIB. This would be with a adapter so I would not need to build my own.
Probably not... What kind of "adapter"? A GBIB controller? That usually requires a driver (running on a computer). And, any software development kit (that works with the driver & controller) will probably also be designed for a computer.
It would probably be easier to build your own GPIB controller... Not easy, but easier... There are GPIB driver chips (75160 & 75161) and GPIB interface/controller chips (7210), and probably others, but you still need a microcontroller.
The tricky thing with a project like this is testing & debugging. If the instrument doesn't respond as expected it's almost impossible to track-down or narrow-down the problem.