BLU is considered a 'limited job', meaning it's restricted from most other content above level 50 and from the duty finder. Their skills are specific only to BLU - you can't give them over to other classes or jobs, you can only use them as a BLU. Lucid Dreaming is an exception, as it's a role action available to all Caster DPS jobs (Red Mage, Black Mage, Summoner), which includes BLU.