a barbarian with rage + raging vitality gets how many temp HP?
It appears to me to be +3 hp per HD?
Yes, the +6 bonus to con from rage with raging vitality, grants an effective +3 hp per HD.
To clarify, while temporary, these are not temporary hp (like you get from false life).
The hp from rage is added to your total and current hp. When you loose the bonus they are substracted from your total and current hp again.
Thanks :)
Real answer to OP: none.
Those hp are REAL. Which means they can be healed through magics.
But your calculation is correct: a total of +3 hp per HD. Also remember that fort saves also increase by 3.