On: Reasons why Apple should add "Gift This App" to iTunes

If they are beta testers, why do they need a code?

I'm not sure but I would assume if once the app is released, they can't even reward the beta-testers by giving them the app they helped build.

Just let them install the last beta, the RC which was submitted to the App Store. They only difference is if they never bought (or didn't use a code), they can't rate it on the App store.