There is intent, and there is technical implementation of this intent which sometimes can be flawed. Please correct me if I'm wrong somewhere, or if something in reality doesn't work as the described intent. This should work the same in each dungeon.
If you are locked out from content this means (you have lockout for one or more bosses):
1) If you are leader of the party, boss and every add connected to him will not spawn when you enter instance - this allows for "saved progression" if you need to go out and want to get back to your dungeon later.
2) If there are 3 or more lockouts for the specific boss you just killed nobody in the party will get loot.
3) If you are not a leader and you or your party kill boss you should not obtain loot.
4) If you are not a leader and you or your party kill boss you should not obtain quest credit.
5) If you are not a leader and you or your party kill boss you should not obtain any influence.
It's also good time to report any issues with the above, otherwise we might be forced to wipe the PvE gear from the players

.
Now to answer your questions:
1. It should not count.
2. No, it should not work like that. If you are locked out, you are locked out. You can enter the instance only to generously help others get their gear and you should get nothing out of it except content that is not locked out (drop from adds, crafting supplies, stuff like that).
3. The limitations are that when you are locked out, you are locked out - no progress for the main dungeon reward should be available when you are locked out. Again, you should only be able to help others, but not progress yourself.
4. The intention is that this should work in all dungeons.
After yesterdays hotfix it should work as above. Can someone correct me if it does not?