I just got temporary custody of my 2 mo old grandson (and his 2YO sister). It was really all I could do to NOT offer him a breast the 1st time he cried! I KNOW I could have relactated, and my breasts still ache when he cries, but I fix a bottle of the stinky formula. I think if I knew he would be staying here, it would have been harder, but the theory is his Mom will get him back. I already am concerned that he is getting used to co-sleeping, and will be expected to be in a crib when he returns. (Sorry, I just can't do the crib thing, and as a non-official foster parent, I can make my own rules, for these babies at least).
Interestingly, and in a way related, I cannot get the 2 YO sister to cosleep. I would much prefer to have the babies with me - that is how I have raised my Dumplings, and it feels safe and protected to me. But she cannot sleep with anyone in the room, sleeps so lightly that anyone's sneeze would surly wake her, and she cries when I have tried to get her to sleep with me. She needs to be rocked and cuddled, sang to and kissed, but then put down in a crib. She cries for less than 30 seconds, then falls asleep. This is all she knows, and I would not be doing her any favor by changing her habit. Much as I think the closeness of cosleeping is important, I have to remember that this is about the babies' needs, not mine.
No one has ever asked if my bio kids are vaccinated, and I never offered any details. But I do have to vaccinate my regular foster kids (I am also a licensed foster home) even if we all know full well that I am adopting as soon as possible.
I appear pretty radical/hippie to social workers, and I have never had any problem in my current area. But is other states, I have been denied a license for silly reasons. I think it all depends on the individual worker, the political climate of your area, and like that.
All the best in your fostering decisions!