"Can 'fake' Democrats really pull an upset" in the Wisconsin recall primaries?

Here in Wisconsin, 6 Republican senators are facing recall elections, and there must be a challenger in that election. How is it determined who that challenger will be? Republicans are forcing primaries by fielding Republican candidates vying for the challenger position in the recall election. This apparently isn't just a delay tactic. Wisconsin has open primaries, so there is nothing stopping voters who like the current Republican senator from showing up at the primary and voting for a Republican challenger instead of the Democrat, which would make the ultimate recall election a battle between 2 Republicans.

... Mordecai Lee, political science professor at the University of Wisconsin-Milwaukee, [says] the primary elections are likely to have very low voter participation, and low-turnout elections tend to attract more conservative voters than high-turnout races....

Charles Franklin, a political scientist at UW-Madison, considers the likelihood of a protest-candidate win as "remote but not impossible."

"What makes it remote," he says, "is that it requires a tremendous amount of coordinated effort" to educate voters on which candidate to favor, and then get them to the polls.

It seems to me that the whole idea of recalling a senator is a protest, and anyone trying to unseat him might as well be called a protest candidate. What makes the Democrat challenger "real" and the Republican challenger "fake"?

If, as Franklin says, it's hard to educate voters, why would that problem favor one primary candidate over the other? We're talking about districts that went Republican in 2008, which was a strong year for the Democrats. Why shouldn't the people who want a Republican senator head over to the open primary and vote for the Republican? I think a lot of people are irritated that recall elections are happening at all, that Democrats have failed to accept the results of the last regular election. These people have every reason to come out to the primary and protest against the whole misguided recall movement.