Of course he is. Do you think he wouldn't approve a moderately conservative justice? He's telegraphing to Obama that anybody left of center has no chance, and maybe even a moderate has no chance. If Obama wants to get another pick, he should nominate a slightly right-of-center judge, which, for liberals would be a big improvement over Scalia anyway.
Trying to use Senate obstruction of a liberal nominee as a campaign talking point isn't going to work. I suspect Democrats think so, but the typical voter, and especially the typical swing voter, couldn't care less about that sort of thing. It's especially not going to work now that Republicans have Democratic hypocrites (e.g. Biden and Schumer) to use as a shield.
It's a game, and the Republicans are trying to move Obama as far right as possible. Of course, Republicans aren't holding very good cards. Although I think Trump is likely to beat Hillary, he's also about as likely to nominate Howard Stern to fill Scalia's seat as he is a conservative.