No, they're from us, reworded by me.
"If I keep my unit of Necron Immortals in Reserve, are they allowed to enter play via the Monolith's Portal?"
No, the Monolith clearly states "If a unit of Necron Warriors is eligible to enter play from Reserve" - this does not permit other units with the 'Necron' Special Rule to do the same. Note also, that unit of Necron Warriors must be declared to be entering play through the Monolith at deployment to be eligible for this method of battlefield insertion.
"In my unit of Space Marine Scouts, I have chosen to take the upgrade character Scout Sergeant Telion. He already has the Scouts Universal Special Rule, which is provided by the Camo Cloak option for models in the squad. Does this mean he doesn't have to pay the points for the upgrade?"
Unfortunately, no. This is a stupid error, that forces you to pay the points for an item that serves no purpose, as he already has the Rule. Sorry. You must still purchase cloaks for every member of the unit, or none, however.
"Can I use re-rolls to wound granted by the Eldar Psychic Power Doom on successful rolls?"
Yes, although this is only statistically viable on opponents wounded on a 2+ by a Rending weapon that failed to roll a 6, and would otherwise grant the enemy an armour save.
"Are Hot-Shot Lasguns affected by the Order First Rank Fire, Second Rank Fire?"
No, Hot-Shot Lasguns are a different weapon from Lasguns. The order can be issued to a Stormtrooper squad, but they will receive no benefit.