It could create more minijobs but no necessarily so. cleaning up minor sand mounds is a job that could be handled the same way that blood cleaning is done now. No need to assign specifically any dwarfs to it. Big mounds of sand, which effectively act as rock walls, could be dispersed into minor sand mounds by miners just like if they where digging up a cave in.
Besides, a good cave-fortress in the dessert would be dig far down into solid rock where there's little amount of sand. Not just built near the unstable sand surface.
Just imagine this:
The adventurer almost reaches the core of the abandoned fortress of the late Urrīt dynasty. Where the rumors say that lies the treasure rich tomb hall. Just ahead lies an open space with the floor covered in sand. No creatures or beast appear in sight.
The adventurer takes a few steps into the sand when suddendly he feels his like walking over a soft mattress. Only that this "mattress" of sand is starting to engulf him. Late to break free, the adventurer wonders worryingly if his quest will end sunken in the desert.
A few agonizing minutes later the adventurer falls into another chamber filled with sand right below the one he was before. Feeling and outburst of joy, the adventures starts laughing without realizing that this new chamber has no apparent exit, and the sand surrounding him is shaking softly. Revealing four giant scorpions just recently awakened by his laughs. Maybe the idea of a death by suffocation inside the bowels of the dessert wasn't so bad after all.
[ August 03, 2007: Message edited by: Zemat ]