Interesting question. Before arc 4, as a person? I'd say no, probably not. If anyone was aware of how weak Subaru was and how much he was fronting it would be Roswaal, most of his plots were to build Subaru up to be a tool to push Emilia on to the throne. It's really hard to say though, Roswaal tends to play things close to the chest.
After arc 4 its harder to say, where before Subaru was merely a tool to be used he has now become the guide for Roswaal to achieve his overarching goal, he probably respects him more though.