Oh yes and it works quite well. Not only does it help with coat health but it also helps with hoofs and whatnot. You can usually get it at your local feed store or Co-op. It shouldn't have any ill side effects...but like all new things just test it out.
As has been mentioned, the BOSS has ample Omega 6. Flax has Omega 3. Most horses kept on pasture will get Omega 3 from fresh grass. Horses who do not have pasture available will be lower in O-3.. Pastured horses being fed hay in winter will not have the O-3 at that time from the grass either. I think either is fine for putting a shine on, but you may want to check to see if your horse needs more O-3 instead. I've fed BOSS and all my horses love it..