I haven't had a chance to try this glyph out as yet, and when I do I'm not sure how I would tell, do the stats of the equipped weapon(s) make any difference? What about enchants, gems and reforging? Or is it meant only to provide a different appearance for the Felguard?
No, the statistics on the weapon don't matter. The purpose of this glyph is to allow you to customise the aesthetics of your summonable pet by changing the weapon it wields. Many of the weapons that are recommended for the looks at the time this glyph was first added are, in fact, level 60 raid gear from Vanilla.
As the statistics on the weapon don't matter, neither do gems, enchants, or reforging.