According to page 2 of the B5 RPG and Factbook, the following is Open Game Content:
All character statistics and creation rules
All new character classes and Abilities
All new feats, powers, and skills
All rules systems and mechanics
All statistics blocks and paragraphs specifically explaining rules mechanics or special qualities.
The use of product identity in these circumstances is limited solely to to mechanical effects of the system, not to the items previously stipulated as falling under PI.