Maybe?
When you get hired in a creative capacity, usually it's in the contract that you're basically creating things FOR the company. You don't own them, and you know you won't own them going into it. So when Ramsay did that design for Murphy's he probably knew that he wouldn't have any of the rights to the design.
So he created a design knowing full well that Murphy's owned the rights to it and could do whatever they wanted with it afterward.
Is what they did unethical? I really don't know. It's more like one of those things that's perfectly OK for them to do, but kind of sleazy and creatively lazy. Which is kind of how I think of Murphy's in general.