Is Hebrew support built into Android? If so, is it in all versions?
Here is my understanding as a developer:
Android 1.5-2.1: Right-to-left support is built-in, but most ROMs do not contain the letters. This means that Hebrew in most applications will show up as boxes (but in the correct order). This does allow individual applications to include their own fonts and thereby display Hebrew correctly.
Android 2.2: The default system fonts now include Hebrew characters. Right-to-left layout still works. (Although the rules for justification did change, annoyingly.) Based on some bug reports, Google did not yet consider support for right-to-left languages to be final in this version. (Note the comments by Google engineers, such as Romain Guy here: https://review.source.android.com/#change,15955).
Android 2.3: The SDK has been released, but no updates for actual devices. The SDK does include a Hebrew locale for the first time (http://developer.android.com/sdk/android-2.3.html#locs).
Also note that locale support ultimately depends on the vendor of the actual device (either the carrier or handset manufacturer). They may choose to remove locales they deem unimportant to save space, or they may choose to add some that they deem important for their targeted market.
Froyo/Android 2.2 added support for displaying text in Hebrew and Arabic (among other languages), including the needed fonts.
Unfortunately, previous versions do not have Hebrew support in the stock source, though I would not be surprised if a device maker added support to their device on an ad-hoc basis.