Though many have resurrected the Druid path (usually called neo-Druidry), most people are referring to the Celtic culture when talking about Scottish witchcraft. At least, that's the approach I am going to take for this article. Just remember that the Celts didn't live only in Scotland, so some things that are attributed to their culture could also be considered Irish.
Like with many ancient cultures, not that much accurate information has been passed down with regards to witchcraft. Many people have tried to tie modern Wiccan practices to Celtic origins, but that is a little questionable. Do not confuse true Celtic paganism with Celtic Wicca, which is a variation of Wicca that has adopted some Celtic leanings.
People who attempt to follow a true Celtic Pagan path would be Celtic Reconstructionists, who really represent a truer form of Scottish witchcraft though they include a complete religious path along with any magickal practices. They did not practice witchcraft as we consider it today, but had a very nature-based form of shamanism as a magickal practice.
Celtic Gods and Goddesses
The various people who lived in the Scotland area had their own pantheon's of Gods and Goddesses that they worshiped. Here are some of the better known Deities in the Celtic pantheon.
Danu - the great Earth mother of fertility, prosperity and cattle
Dagda - Father god who ruled over life and death, who was particularly worshiped by warriors
Morrigan - a triple crone Goddess who embodies battle, death and magick
Lugh - a Sun god of courage, youth and all craftspeople. His son was the great Irish folk hero Cuchulainn
Cerridwen - a fertility Goddess who also represented knowledge and wisdom