Can doctors ever prescribe herbal remedies?

Yes! There are herbal specialists that are well versed in this science. Many universities are now conducting studies in order to provide evidence based medicine.
Often. If we are totally satisfied with their safety, yes.But we also need to believe that they may help as most products have no scientific proof of effectiveness.
Yes. We do it all the time: chamomile tea, fennel tea, etc. Would we ever use them for a disease that needs real medicine? Certainly not!
No. Doctors prescribe medicines that are regulated by the fda and require prescriptions. Doctors can, however, *recommend* herbal remedies if they are comfortable with and knowledgeable about them.