[Rowana]

If you put a deity in your deity field you are considered devout enough for it to matter, druid or fighter. If a fighter does something to besmirch the good dogma of a deity, the deity will notice but not necessarily punish as they are more a sheep in the fold rather then a shepherd. If a druid, more a shepherd (especially when considering the nature gods) besmirches the faith of the god by abusing their tenants and wishes, there will be actions taken. However it may not be as serious as if a cleric has done such a thing because as you point out, the druid does not rely upon the deity. Yes druids will abandon their chosen deity if it comes in conflict with the land, but who you get to cast your blessings upon doesn't really come in conflict with the land.

As an OOC mechanism, if you are not devout enough to your deity for deity to matter you might not want to put it in your deity field. However as an IC mechanism, Kith, Folian, Katia whom ever, is still going to look upon you as a follower if you claim to be and if you betray them, they aren't going to be happy about it.
~row