If your vault is accessible there, it will be the same one.
Pretty sure everyone knows by now that the space we have now will be expanded, I imagine in a big update before House of Wolves is released (like they did with the bounty slots).
I don't understand why everyone keeps thinking it will be a completely different vault, separate from the tower. Read no end of comments on Reddit about it, makes no sense at all.
it doesn't
but people are suggesting it because it would seem the easiest for them to implement given how hard they made it out to be in the weekly updates.