Inovisible has written an awesome guide for Operative Healers. It covers everything you need to know and explains all the stats diminishing returns and numbers you should be aiming at. He also has a cool Google Docs spreadsheet you can view which is what he used to calculate the optimal values. You have to request view permission on the spreadsheet, he granted it to me with no questions asked within 24 hours which is pretty cool.
One of the main problems with Scoundrel/Operative healers using a stealth revive is that you MUST wait until all of the HoTs you have applied to allies have worn off before stealthing out or it will put you back into combat.
This might explain some of those failed stealth-res attempts, but I guess you already knew that
I already knew about the HoTs effect on stealth revive, that's why sometimes I'll run over to the body but then have to wait a few ticks. I've started trying to do as they suggested by casting the last HoT on myself. Then I know once that's worn off the raid is free of my HoTs.
This hasn't really been a problem with like 95% of the stealth revives, it's just getting the timing right as sometimes just having the phase change will bring you back into combat. Other times its when ads attack or the boss does an AoE, that kind of thing. That's why it's important to get the timing right, that's the bit I still screw up every now and then! Sometimes you just have to do it and hope nothing goes wrong, it really depends on the situation.