I stopped using oats in my beers because of the viscous feel they added. If I'm honest it always seemed like more of a visual thing than a mouthfeel issue but people say you 'eat with your eyes' and the slightly gloopy look pit me off the beer even if they tasted fine.
Now I just use wheat malt, which i find gives a softer mouthfeel without the viscous oiliness that oats leave.