Do pain signals share some of the same transmitters as emotions ?

Of course: We have only a limited number of neurotransmitters and a very wide variety of functions to integrate. It's more realistic to start out with the assumption that everything shares something. Pain neurophysiology is mind-manglingly complex and involves not just button-pushing (neurotransmitters) but a labyrinth of excitatory & inhibitory interconnections at brain & spinal cord levels.