I tried it a one gig a couple of years ago. I plugged into my Sansamp, used a Wharfdale powered monitor and put the sound through the pa. But I found that the sound from the amp was what I missed. I imagine that with good monitors, a good pa and a sound guy, it would be cool.
But there was a good covers band that gigged around my area that had what I mentioned above and the guitar and bass sound was always crap. The drums sounded good though.
There is another thought. If you have to drag a decent monitor around with you, would you not be better having a lightweight bass amp?