Battlerager Vigor: gives you THP if you are hit. There is nothing special about these THP's and do not stack with other THP. This in of itself is a huge bonus, replenshing your THP everytime you get hit.
Invigorating: Gives you THP that stacks with other sources of THP. Follow the THP stacking rules though and they should not stack with themselves.
Nowhere is battlerager Vigor mentioned under invigorating.
Reason why you should keep Invigorating seperate from Vigor THP sources.
Con: 18
Not seperate: If you have 8THP, (4 from Vigor, 4 from invigorating) and you are struck for 4 points of damage. THe the player can simply say he still has 8 THP after the hit because he gets 4 from Vigor for getting hit.
Seperate: Same situation but this time he recieved his Invigorating THP after he recieved his Vigor THP. He is hit for 4 dmg, and looses his invigorating THP but since still has 4 THP from Vigor he can't add more leaving him with only 4 THP.
That's ... not how I read it at all. I understand the temptation to do so, but really the Rager only has a single "pool" of temporary hit points.
He starts with 30 HP. Con of 18.
Round 1: He is attacked by an arrow and takes 8 HP. He gains no THP. He is also hit in Melee for 8, triggering his Vigor.
He now has 14 HP & 4 Temp HP
He attacks with an Invigorating power and hits. He gains 4 more THP that stack with the ones he received before, per the class feature.
He now has 14 HP & 8 Temp HP
Round 2: The archer misses this round. He's attacked in melee and hit for 3. This drops his Temp HP down to 5. His Vigor would only give him 4 THPs, but since he already has more than that, he gains nothing.
He now has 14 HP & 5 THP
He attacks and hits with an Invigorating power. He gains 4 more THP.
He now has 14 HP & 9 THP
Round 3: The archer crits him for 10. He loses all his THP, and 1 HP. He's attacked in melee and also hit, this time for 8. He gains 4 THP from his Vigor.
He now has 5 HP & 4 THP and should probably consider getting some healing.
Instead, he attacks and hits with an Invigorating power.
He now has 5 HP & 8 THP.
Round 4: Both enemies miss.
He attacks and hits with an Invigorating power.
He now has 5 HP & 12 THP.
Round 5: The archer misses. In melee, he is attacked and hit for 6. His Vigor would give him 4 THP, but since he still has 6 THP, it does nothing.
He now has 5 HP & 6 THP.
...and so on.
The important things to keep in mind are that (1) The THPs from getting hit in Melee or Close don't stack with any other THPs, regardless of the source; and (2) The THPs from Invigorating stack with any other THPs for a Rager.
-O