Sometimes, when making this dish for guests or when I'm not too worried about a little extra fat, I use pancetta in this recipe. Just use one thick slice, cubed quite small. Brown it up before you brown the chicken. Remove the browned bits onto a paper towel and use that fat to brown the chicken. You can throw in the pancetta bits with the chicken for braising.
The sun dried tomatoes are not necessary, but I think they add a richness to the flavor of this dish...I love them.
I specify San Marzano tomatoes because they are really amazing. They are sweeter and less acidic than regular tomatoes. Honestly though, if you've got a can of any other tomato...they'll work just fine.