Steal all the vehicles during a siege and have our own Destruction Derby Match. Create a new game on some of the maps. Just like a really old game, play Carmagedon with looted vehicles.
"It's not an exploit. It's a feature!" Seriously though if they can make it be a feature in someway, balance it out with losing one of your actual tank spawns and putting an Orky decal on the side so it's not super sneaky it would suit the Orks down the ground!
I've spawned an Ork Wagon onto the upper tier of C on Torias once. The vehicle bay below the point was there for a second and I suddenly dropped about 10 meters onto the 2nd tier courtyard in front of the point. Weird stuff. Annoying too as I was trying load up a bunch of lads and head to A at the time. Couldn't drive it off the roof and it died to bunch of Space Marine plasma in the end. Waste of a good vehicle. The vehicles are trixie as hell in this game sometimes.
Instead of at the spawner, just make it abandoned vehicles. But as long as someone is inside of it, you can't loot it. We have to protect our rhinos, damn it.!
Loot the shit out of it. Make it open top/remove the dome. tear out the seat and console and slap a new "betta orky wun" and bam, ork in a wave serpent.