Roots will find their way around most rocks quite happily, but remember the
tree wants a root structure that is almost a mirror image of the green bits
above the ground. Have a look at some of the old druid dawings sometime,
they knew about this many years ago when everyone was a farmer of types.

I have a farm in SE Qld, with a lot of side of the mountain rock and cliffs,
a lot of various gum trees and they grow quite happily on the edge of a
cliff bank. If more water is available, they grow well on the top edge, but
if less water, the bottom of the back works well.

The ones that get there roots down to the water table near the creek just
get bigger and bigger!

Hope this helps,
Peter