Alright so after 2 days of fighting with this, I was not able to get it to work this way. I followed at least 10 different tutorials on how to get custom property testers to work, but to no avail. I went as far as using the startup extension point to force the plugin to load early. Used a SelectionChangedListener to request updates from the evaluation server anytime the project explorer selection changed. NOTHING seemed like it was going to make the custom property tester work. It simply would not load the property testers... they would never get called by anything, despite everything saying it was set up fine, and perfectly mirror all the tutorials I followed.
Eventually I got tired of trying to make that work and looked for an alternative. What I ended up finding was this: http://blog.eclipse-tips.com/2009/02/commands-part-5-authentication-in-rcp.html
I implemented a SourceProvider to have a variable with values corresponding to different project states. I then use , and check which of the possible values it is. Finally, when the plugin loads, I hook a SelectionChangedListener to the PackageExplorer's viewer, so that any time a selection change occurs, then the logic is reevaluated and that variable is changed if needed. Although it's not the ideal way I wanted to do it, it works, and it's not deprecated. I simply couldn't waste more time trying to get the property testers to work...
Hope this helped someone!