They could work...but I pity the poor bunch of people who attack both sects of priests...with twice as many shrines around. Perhaps it could be possible to "convert" a shrine, from dark to light, and vice versa?
I also pity anyone going up against Ashtan if the dark priests were around.... having the damger of both convocation AND vortexing would be...annoying, to say the least.
Caled

Penned by my hand on the 5th of Aeguary, in the year 250 AF.