This is such are hard place to be, I have been there and can sympathise.
My advice is....if it makes you feel good (for yourself and your daughter) to keep them in touch with her(via cards/pictures etc) then you should do that. If ever they ask you to stop, then stop. They are your daughters family and some day they may come around. It is unfortunate that they don't see the treasure they are missing out on, but hopefully some day they will see the light. Have you talked with any of them to find out what exactly the problem is? Spend the time enjoying her, and your own life, and don't worry about what they are missing out. Let her be around people that WANT her around, that can only be good.
Even though my son's 'other' family has little to do with him, I encourage a relationship, I never want to be the one who stood in the way of a relationship. Also he has two little sisters(half) and its through the family that he is able to see his sisters. Of all the family he doesn't see, its his sisters that bother me the most. I couldn't imagine having sisters and not being close to them. I would love for them to come to my house and visit, but they live quite far away.
We all get along(we are not friends) but we can speak with each other. Even though he only sees them a couple times a year, I know that he would be missing out on a great family if I didn't allow him to go. The only difference is that my son's 'other' family accepts him(there are no doubts).
As far as the deadbeat dad goes, regardless of whether he sees his daughter, he should pay child support. My son sees his father about once or twice a year and frankly he is an IDIOT! But I never say negative things about him to my son because he loves his dad nonetheless. I don't want him to grow up hating his own father. Actually I don't dwell on it, I used to. We live our lives and his dad calls a couple times a year and we move on.
He finally started paying child support a couple yrs ago, which means very little, I really just wish he would call more often. I know my son misses him sometimes. He is the king of broken promises which of course is nothing new with deadbeat dads....its so hard for the little ones to understand.
Wow this turned into my very own rant, rather than supportive advice. Sorry.
Bottom line, do what you feel good about doing, you can't control them, just gently try to encourage a relationship, family is important. Sounds like you know what your doing, keep it up.