The creator and game director for Street Fighter X Tekken has said that both systems will be able to 'share' the DLC
Firstly Yoshinori Ono has confirmed that DLC will be available for Street Fighter X Tekken, and that the PS VITA will also have downloadable content available.
However Ono has said
"Yes, they’re are different hardware but they’re are part of the same PlayStation family, we’re already talking with Sony about ways to sync both of them together. As long as you’re using the same PSN account, things you’re purchased on the PSVita will work on PS3 & vice versa."
This is great news, it confirms that you will have the ability to share the exact same PSN account with your PS VITA, and with Street Fighter X Tekken whatever DLC you purchase on the PS3, will then be shared with your PS VITA. So there is no need to pay twice for the same DLC.
Everyday we see more and more compatibility with PS3 and PS VITA. Sony seem to be working very hard with features such as "Transfarring" (yes it does sound stupid, but its a great feature)
Be sure to check www.psvitahub.com daily for all the PS VITA, news, reviews, videos, and game trailers!