Whatever you use to grow your plant in is your medium, whether it is potting soil, grow rocks or rock wool. Re-phrase your question.
Absolutely. There are many methods to germinate seeds outside of soil, then plant them once they "pop". This way, you are not planting inviable seeds. Depending on your style of growing, this can be very important. The Cannabis Cultivation GrowFAQ - The Internet Hub for Marijuana Cultivation - Seeds, Germination & Seedlings