I've heard of the Shadow Creature template, but Hairy Spider is new to me. What book is it from?
A mimic with five Druid levels can turn into a wolf for a few hours, summon apes, and cast dominate animal or wind wall. An elf with twelve Druid levels can be a shambling mound all day, summon elephants, cast liveoak or wall of stone. Losing a few levels of spellcasting won't make a druid (or any other caster) incapable, but it will make them less capable. I'm not sure the mimic's abilities make up the difference, and they don't really synergize with druid abilities.