Absolutely. I don't know if you've figured this out already, but the easiest way to rack up a high combo is to just strike one thug, then move to another, then move to another, and keep doing that so you're constantly putting them down and not giving them a chance to gang up or attack you.
Oh, and here's something that confused me: Do the combat challenges scale to your difficulty setting? I thought they did, but then I started a hard game and tried a combat challenge after playing through the story for a while, and the thugs had the little blue warnings, even though they don't in story mode.