Soot is the primary cause of rapid oil blackening in EGR equipped diesel engines, not the EGR system itself. In the industrial and heavy equipment world, the Tier 4 Interim engines were /are the worst. These were pre-SCR (pre DEF injection) engines that used overfueling and EGR to lower combustion temperatures to reduce NOx and meet emissions. They produced more soot from the overfueling, and then recycled that soot laden exhaust into the intake system, leading to high soot concentrations in the oil. They have a tendency to plug EGR coolers, coke valves, and plug DPF's. SCR engines (Tier 4 Final) use DEF injection for their primary NOx reduction strategy, and consequently don't have the overfueling and high soot production issues of the T4I engines. There's still EGR, the oil still gets black as soon as the engine starts, but it's LESS of a problem.
In contrast, gasoline engines running at or slightly leaner than stoich don't make soot, at least none worth noting. You'll see as much or more contamination of the intake tract from the PCV system as the EGR on most gasoline engines. Blowby is still the primary cause of oil contamination and breakdown, but is present in all piston engines and is just a given.
Here's what you need to do: build a draw through turbo system for your LPG rig, and get an Altronics NOx feedback system to kick in and control fueling during steady state cruising. That will accomplish the same thing as EGR as far as combustion temp reduction, increase your fuel economy on LPG, and make for a cleaner, more environmentally friendly truck overall. Not to mention a healthy horsepower gain over an NA LPG engine. You'll only need to fabricate your own draw-through LPG and turbocharger setup, and cobble together the control system from the factory ECM and the Altronics system. Small potatoes, right?