LOL...
I've seen it before. Never on a GP. 92-96 Supercharged Bonnevilles had it. You guys know..while GP's were suckin with 3.1's...lol
I'd expect that to run to the driverside of the radiator into an oil cooler, just like the stock trans cooler, but for oil.
Oil cooling is very effective in cooling a motor. Some say it's nearly as effective as water cooling.