I've just spent two days sitting in a field re-reading Paul Bennetts excellent The Old Stones of Elmet.
Paul comments upon the frequent occurence of this name in the England. He remarks that "considering that personal names, when applied to hills, are of such a rare occurence, we must look for another solution"
Paul explores the druidical links looking at the druidical tradition and Simon Magus.
I found this in the online etymology dictionary "Simon, which is from simos "snub-nosed."