So long as the right-handed soul-brother grip is kept between the bodies during the hug, there is no question of sexuality. The left-handed fist bump into the back goes a long way in furthering this image.

Now, the ass-grab, on the other hand, can be crossing the line - though my one buddy has a tendency to go for it often, but I don't think his wife is giving it up as often as she should, so I cut him some slack on that front.