I am wondering if the three row accordion is ever used in Cajun music and not just Zydeco. I am semi confused by the two labels because the styles are so similar but I think there are some differences. Related to this are there any Cajun groups that are more bluesy or would that automatically Zydeco? Would Cajun music played by Creoles automatically be Zydeco and Zydeco played by Cajuns be Cajun?

I'm sure there are bands who play cajun songs on a three row and even on a piano accordion. This could be a very interesting subject :-)
Original Cajun music is played on the one row since the accordion was introduced in Cajun music. The so called Creole music is also played on the one row, but also the two and three row was used there. An important part of Cajun and Creole music is the fiddle.
In Zydeco all accordions are used and in the early years there was Clifton Chenier with the piano accordion and Bozoo Chavis with the diatonic accordions. Those three genres are a melting pot of how to play it and it's changed over the years.
I prefere Cajun and Creole, but Zydeco is the best side-effect I know :-)

Right off the top of my head, I have recordings by File, Beausoleil and Steve Riley using the triple row accordion. If I thought about it for a while, I'm sure I could identify more.

-David