I have just tried to use Brilliant Gallery from 6.x-4.4 all the way back to 6.x-4.0.
None of them support the random syntax, i.e. when I refresh my page, the images shown are exactly the same and not randomized.

I am using this syntax
[bg|photo|9|100|random|9]

The same syntax works fine and photos are shown randomly using Brilliant Gallery 6.x-3.5 or 6.x-3.6

This bug maybe similar to
https://drupal.org/node/1919526