Scotch moss is not going to do the trick. First, it is not a moss at all but a low mat-like plant with a mossy appearance. It prefers full sun, rich soils and even moisture - conditions it is unlikely to receive underplanting pines. You need something suitable for dry shade - perhaps rupturewort, Herniaria glabra. It will need watering to get established and will take occasional but not constant foot traffic. If this is a high traffic area, you might want to consider pavers surrounded by groundcovers.

Thank you for the advice gardengal. I was not familiar with rupturewort but after reading about it, it sounds like it is definitely worth trying since it meets all our conditions. Gracias.