Shock air cans run pretty thick lube oils, gravity isn’t going to help a huge amount, and working them distributes the oil pretty well.
Forks do run much thinner oils, but the bushings wipe so much oil off the stanchions due to such tight spacing that the wiper seal and oil soaked foam rings do a lot of the work preventing dirt ingress and lubrication in the top half. Various forks over the years have used bushings with slots. No current offerings I’ve seen have used slotted bushings, fox have in the past.
As to floating pistons in shocks, the piston has at least 150psi of gas behind it. It will work in any orientation.
Frame clearance is the bigger concern with shock orientation. Angle grinders are your friend!!!
Do regular fork lower and shock air can service. You can’t over service them people. There is a shortage of spares looming for rockshox thanks to covid.