In some cases it is, in others it isn't. For example, my farrier typically has his dog in the car when he comes to my farm, he keeps her in the car, but I would be fine with her getting out and running around if he wanted to let her out. My horses know dogs and the worst that would happen is the horses would chase her, she knows horses so she would know to get out of the way.
I was also pet sitting one holiday (I believe Christmas but maybe thanksgiving) and asked the owners if they would be ok with my taking their dog to my parents so he wouldn't be alone (they were pretty adamant that someone be with him nearly at all times) and I could still go enjoy my family, they had no issues with that, so I loaded him up and took him with me, he laid down in the floor and pretended to be a rug the whole time, in this case, my parents had cats, but they were used to dogs and didn't bother him, and he didn't bother them so there were no issues.
I also have a small dog that is not house broken and will fear bite. I will occasionally take him to my parents house but I keep him on a leash and near me so I can keep an eye on him and keep him out of trouble, there are no issues in that case either as I know his problems and don't let them be an issue at their house.
In any of those cases I could see it being very rude, if my horses weren't used to dogs or the farrier's dog was trying to chase and bite my horses, if the cats had been afraid of the dog I brought for the holiday, if I let my little jerk loose to terrorize people. Any of those cases would be easily turned from a perfectly acceptable situation into incredibly rude in a heartbeat if 1 or 2 variables was changed.