Interesting question! Let's start with checking what the rulebook says.
Dark Ages vampire, page 113:
A practitioner of a Road possesses a certain aura, a personal
bearing, a palpable force of presence that embodies the
Road’s ethos. For characters high on their Roads, this gives
them a reduced difficulty on rolls due to their confidence
and grace in these situations.
For the basic Aura description this is clear. Your aura is a permanent bearing. It can lower rolls because of confidence and/or grace (and/or experience) in certain situations.
Aura modifiers definitely apply to relevant Social rolls.
However, with Storyteller discretion, a character’s aura
might affect any roll with which her character’s bearing
should give an advantage or disadvantage. For example,
a character on the Road of Kings might get her aura
modifier on Willpower rolls to resist forced subordination.
As a Storyteller, favor allowing dramatically appropriate
benefits from auras. After all, maintaining a high Road
score can be a challenge; the player most certainly earned
the benefits
I assume it's this part that started the discussion. So yes, aura bearing can indeed affect disciplines, a Road of Kings character would gain it for resisting majesty from someone who is a "lesser" to them.
But let's transfer the example: Your aura makes it easier to stay on the path you set for yourself and you're not easy to sway. Which means every time you have to roll in order not to be swayed or influenced - your modifier applies. That's mostly Willpower rolls, of course, but your GM could decide to let it apply for other rolls as well. Like a Dominate "Stop!" if you are set on continuing.
Does this mean you get to modify every single willpower roll you make, including blood magic? Definitely not. The situation still has to fit and "I really want to use a spell so this is dedication!" is not an excuse.
Now ...if you really NEED to use a spell because it's vital to your goals or if you'd normally get a negative modifier for distraction ...That's a different story altogether. In such a case your GM could allow it for your spell as well.
But you do not get the modifier for all your willpower rolls and your social-primary Ventrue does not get the modifier for each time he tries talking to somebody.
