In my opinion, there is really very few differences and conflicts between any of the spiritual paths at the core level. The conflicts come into play through humanities sometimes frail interpretation and our inherent competitive nature. Unfortunately, we as humans have a tendency to fall prey to believing that what we believe is true according to our individual mind set and that someone who believes differently is wrong. This weakness is at the center of almost every major conflict throughout history.
If all things are created of and through the divine, then why should working toward achieving and maintaining harmony and balance with the earth, nature and the Divine be something that would bring eternal damnation.
While many of staunch faith will argue the point, it is easily proven through historical documentation that the Bible as we know it today was manipulated during the middle ages. This was a time of very limited understanding and great fear and superstition. It is also the time when the church was a very political organization and was out to convert those of different spiritual beliefs by whatever means necessary. This was initially done by adopting many of the European Pagan Holidays and deities as Saints, and later through the use of fear as seen in the inquisitions.
While the time and space limitations of this writing prohibit going into full detail, it is pretty easily verified by doing cultural and historical research if one puts out the effort to truly understand.
If one goes back to the earlier writings and manuscripts of the Essenes who are considered to be the first Christians, we get a truer understanding of the wisdom Jesus was trying to impart in his advice to us in walking a pure spiritual path. The Essenes as well as almost every native culture you choose to look at all understood our connection with the earth and nature as being an integral and necessary part of our connection with the Divine. They understood that without that connection and reverence, we cannot fully experience being one with the creator and all that exists because the spark of God exists in all things.
We have forgotten this wisdom and forsaken it for a patriarchal system wherein the earth, nature and lives of our fellow man through God's creation is no longer seen as sacred. It has become something to be exploited by a few for earthly gain and monetary wealth with little regard to the damage we do to our brothers and sisters as well as our own life support systems.
I apologize for rambling and I could go on indefinitely and tie so many things together in these thoughts. In direct answer to so many of your questions is yes it is possible to be Wiccan, Pagan, Shaman or Witch and Christian at the same time. The word for this is Eclectic. But in the end, these are only words which mean nothing in the grand scheme of things. In my humble opinion, acknowledging and seeing our connection with the Divine through the earth and nature as well as our brothers and sisters is the very essence of God's or the Lord and Lady's message to us. How we interact is the true measure, not the name we give to ourselves.
The creator is not some far away entity that we only achieve connection to when we die and go to Heaven, Summerland or Valhalla. The creator is here now in everything around us and we are linked to divine energy through all that exists. I fully believe that the creator intends that we should see divine presence in everything around us and continually strive to maintain harmony and balance with all that exists. In doing so, we are worshiping divine presence in the most sacred way. We as a species need to get past the connotations a man given name or title and simply become human. We need to see the divine in everything and everyone so we can evolve and achieve our true spiritual destiny.