I don't really know much about the rubberlip but I did find this little write up on it.I have never heard of one attacking a goldfish up to now.
Chaetostoma sp. Rubbernose Pleco / Bulldog Pleco / Rubberlip Pleco
Adult size 3"-5? (7.5cm ? 12.5cm)
Good overall cleaner: Green Surface, Brown/Diatomic; Generally won?t damage plants
The Rubbernose is a good algae eater for 10+ gallon aquariums. This is supposedly a rather timid fish, so don?t expect to see much of him unless adequate refuge is provided (a fish with more places available for hiding sees the need less). Smooth rocks and rounded gravel are preferred. It is not recommended to keep this pleco with aggressive or high-activity fish.
I personally always supply either a wooden hiding place for my plec's as they look camoflaged against it.Or I make a nice area with plants and a small kinda den he can hide in.My hong kong plec hides in a large head shape ornament during the day.which has plants on it.Where my common plec in my tropical tank I made him a den using a peice of slate and some rocks with him being large and clumsy.
Personally I like the hong kong plec.Hope this helps you anyway.