Nope. If fighting for what is right is the right thing to do, then a Hufflepuff can be counted on to fight. After all, not fighting when fighting is the right thing to do would not be the right thing to do now, would it? And you yourself wrote that a Hufflepuff can be expected to do what's right, no?
Standing and fighting in this case isn't so much doing the right thing as it is trying to stop the other guy from doing the wrong thing. Statistically speaking, a Hufflepuff is more likely to run and hide, since the stand-and-fight response is not a selection criteria for Hufflepuff, but it is for Gryffindor. As a primary selection criteria for an entire house, it can be predicted that the courage trait is generally underrepresented among the other houses.
Statistically speaking, the Ravenclaw is more likely to be an interested spectator, while the Slytherin (assuming they didn't start the fight in the first place) would likely monitor and prepare to take any action based on self-serving opportunities.
However, because people are complex, we can expect that anyone who tests highly for the traits of courage and empathy will join in the fight, regardless of their House (see Snape, Severus).
