JW funerals sometimes have pallbearers, sometimes don't.
Being a pallbearer for a non-JW funeral would be the sticky situation. Is the funeral in a church? Even if it's in a funeral home, is it conducted by a minister of another faith? Are there some traditions performed that would be considered "pagan" by JW standards?
I was a pallbearer in a non-JW funeral. This was when I was first making my exit from the JWs. When I was first asked, I had a sense of dread and fear. How was I going to get out of it without hurting feelings? But then I realized that I wasn't playing by JW rules anymore and I accpeted. There was a feeling of enpowerment for doing what I thought was right and decent instead of allowing the fear of the WT teachings to dictate my thinking.