DH...to my knowledge, no, except in the 6GR qualification test (but that's only an unstated, default access angle, not the electrode angle, though it does dictate that somewhat), but after qualification, not restricted.
In some weld profiles, the angle of the electrode is key to getting a proper weld profile. An example would be a horizontal fillet weld.
Besides, it would have to be specified as an angle in at least 2 planes, which would be difficult to monitor and control.
I don't deal with AWS on a daily basis anymore, so hopefully others can confirm or set me straight!