I know this has been addressed before, but how exactly do summoning alignments work? If a cleric is lawful neutral can he summon a chaotic evil creature like a fiendish crocodile?
Nope, he can't summon a chaotic creature. The spell which summoned it would, in turn, be a chaotic spell. A cleric cannot cast spells who's alignments directly conflict with their, or their patron's alignments - if the cleric was true neutral, but was the follower of a lawful god, they couldn't cast the example spell either. A druid cannot cast spells who's alignments conflict with their own alignment.