I did a quick test. This is a clip of a new song from my band. The first clip was done with a MusicMan Stingray 4 string tuned to A#. The 2nd is a PRS Custom 22, both pickups selected (Tremonti Treble in the bridge, Dragon II in the neck).
MusicMan Stingray 4-String Bass
Pitched Guitar as Bass
There are 3 tracks of bass in each example: DI, Bass AMP, Bass DIRTY.
The Stingray was DI'd into ProTools and run through Ampeg SVX for the amp track. For the dirty track, it had a slight compression on it, then it was run through the TSS plugin into LeCab with the Catharsis Fredman impulses.
I had to realign the tracks by hand because of the delay introduced into the Amp and Dirty tracks from the plugins. The phase also needed to be flipped on those tracks. They were then compressed and eq'd to taste. The Dirty track has an exciter throw on it with light settings.
For the pitched-guitar-as-bass track, I ran the guitar direct into PT8 and tracked the part. It was then pitched down with Melodyne, and then ran into the RedShift Pickup Replacer on the "Generic Bass Gtr Single." From there, I applied the same amplification and distortion settings as the other tracks and compressed and eq'd them to taste as well.
My conclusion:
It's hard to replace a nice, real bass. There's a lot missing in the pitched guitar tracks. They don't have the spank and growl that the real bass does, of course a lot of that is the "MusicMan sound."