Neutered males can only have an erection if it is not due to sexual arousal. When a man is neutered it removes all desire to procreate and hence he has no will to get aroused. The only way a man can have and erection when he is neutered is to have a urinary erection, meaning he has to go.
Coming from a man who was reciently "snipped", yes you can still have an erection and preform as good as always. You also still have ejaculant or cum after climax. only 3% of ejaculant contains sperm.
I think the term neutered can only be used for animals. But rarely dogs can still have a possible erection. Sex drive will be totally killed but the dog's personality will tell it to act sexually with a couch or a your leg.