You know, this is something I never understood, and it has been one of the biggest things for people to blow out of proportion. In Episode I, Watto never said anything about being immune to the Force. He said, and I quote:
"What? Do you think you are some sort of Jedi waving your hand around like that? I'm a Toydarian. Mind Tricks do not work on me - only money."
To me, that's akin to saying something like, "You can't lie to me. I'm Sicilian. I know how to lie better than anyone."
It's the same thing as saying, "You can't bull$hit a bull$hitter."
A Mind Trick only works on the weak minded. Basically Watto is suggesting that using a Mind Trick on a Toydarian is like trying to lie to a Sicilian. He's not saying he is the countermeasure to the Force and the Force doesn't work on him because of his species. Frankly, that entire line of thinking is just stupid. He's saying that his species' culture has provided him with a mind sense that is unusual to the rest of the galaxy - just like how Sicilians and how the old Italian mobs used to work where everyone was lying to one another and keeping secrets. That's where the stereotype comes from.
Mind Tricks not working on a species is a relatively common thing. but it has nothing to do with them being Force Immune or Resistant. Hutts are known to be the same way as a Toydarian. It's because they're always angling for the upper hand. They're constantly performing incredible acrobatics of logic and reasoning. This leads to someone who is not weak minded. Watto does the same thing in business. Just look at the totally convoluted bets he continued to make with Qui-Gon. All it means is Toydarians have a culture and temperment that makes them strong minded. I guarantee you that Qui-Gon could have Force Choked Watto's ass and it would have worked just fine.
That being said, I would say to ignore completely the entire notion that they are even Force Resistant, and I don't see any reason why they couldn't be fully trained Jedi with the Force as a very powerful ally.
Of course... that's just me.
Edited by Raice