In regards to the comment from 2016 by EnvyEyes; don't wait until the mount "casting" has finished to try and use Sneak+Hide. Instead, do the following:
1) Start summoning a mount.
2) While the casting timer is moving, quickly activate the Sneak and Hide skills.
3) You'll end up mounted with full Rogue stealth (including any Shroud of Stealth AA skills).
A few observations:
- This method will not work with any mount that is 'instant-cast' (I'm not aware of any, except the Pal/SK AA mounts, but those don't apply here).
- This method will not work if you try to put the 3 actions listed above into a macro or social hotkey, they have to be 3 separate hotkeys (one for the mount, one for Sneak, one for Hide).
- I don't remember if this worked when the Tiny Cloak of Darkest Night item was first introduced, but it has worked since I returned in 2015.