I agree that redcat's manuals need to be MUCH better.
supplying a nimh with a brushless vehicle is done by most companies (look at traxxas)
The reason redcat sets the ESC to LVC out of the box is because they feel many of their buyers are very new to the hobby and may buy a lipo not knowing that it cannot be fully drained. Imagine if you didn't know, had bought a $50 lipo and on the 1st run ruined it?
Setting LVC on with nimh batteries wont hurt them.
The bigger issue is that redcat's nimh packs are hit-or-miss. Ive run them in brushless and had 8-10 min runtimes, while others get just a few minutes. Not all of there packs have good enough solder and connections...which lowers the voltage output under load and thus the ESC will low voltage cutoff.

Unfortunately, selling the pro's with a lipo would add $30-$50 to the cost. I know it should be less, but it just isn't. Lipo chargers typically cost more (especially more than a wall brick charger like the pro's come with) and lipo packs still cost more than nimh packs.

I don't doubt that a time will come when redcat will switch all their brushless models to ship with lipo packs. Many do. But to hit a price point, the pro's still ship with nimhs.

To be blunt, I put brand new redcat packs on ebay or give them to youngster's who are new to the hobby whenever I get a new redcat. (nimh packs I mean) and then I just run lipos I buy off hobbypartz.