Originally Posted by: ShootaMcgavinInstead of using the A minor pentatonic over an A major I-IV-V pattern, I read somewhere that one was allowed to use the A Minor Dorian scale with a flattened sixth instead of the A Minor Pentatonic.[/quote]
1. The dorian mode has a major 6th degree, not a minor 6th. It is the only difference between a minor diatonic scale and dorian. So it sounds fine when you play it over a blues; the major 6th (F#) of the A dorian mode is the major 3rd of the IV chord (D7).

2. You are "allowed" to play anything you want. :)

The real issue is: what sound are you trying to create?. In other words, which scale (or mode of it) best suits your musical intentions?
[QUOTE=ShootaMcgavin] The Dorian minor looks like the Minor Pentatonic with the exception of a few notes, but there's a slight problem: A major's Dorian is in B.

This tutorial covers the basics of the modes:

http://www.guitartricks.com/tutorial.php?input=370

I recently posted in depth about the modes here:

http://www.guitartricks.com/forum/showthread.php?t=29705