Hey H G,
RF 5.0.0.Alpha1 ~= RF 4.3.2.Final
It means there is no specific support for LESS/Bootstrap.
There are some more details in roadmap: https://community.jboss.org/message/823882
We were able to prototype support of Bootstrap in Sandbox:
However we are focusing on leveraging full potential of LESS and Bootstrap family in RichFaces 5.
Alpha2 will bring first fruits.