It's a risky move; if they're both introduced at a young age I've noticed that most plecos will get along just fine (assuming the tank is large and full of decor/hiding places..... Introducing a smaller one to a larger could be an issue; but at the same time you know the temperment of you current gold nugget. Some are obviously more aggressive than others. I would say that if you're going to try this, make sure you keep a close eye on them and watch them interact; especially considering a gold nugget isn't a very cheap fish.