I don’t see mikey doing this moveThe carpet idea could work, if you're committed to pressure washing it every day. Until you've had a sticky surface at the back of a box truck you have no idea how much guck gets sucked up from the road.
Grip tape is great on a flat surface, but will not adhere well to diamond plate. It will peel of in chunks.
Do not use the Rustoleum spray-on bed liner! It's brittle and doesn't adhere well. I think it's meant to be used where you want the look of a tough surface, but never have anything contact that surface. Herculiner or one of the other roll-on bed liners would be better for the purpose. Might be worth checking with a local Line-X guy to get a price to coat the bumper, that stuff is tough and has a pretty grippy surface. (Note, you'll never be able to completely rinse detergent spills out of it.)
Maybe try shoes with a grippy sole, or be like Mikey and just parkour roll in and out.
I know, this thread is really making me look like a wimp.