If he refused to allow them to search his buildings wouldn't that put him on their radar? I understand he'd have the legal right, but I'm assuming they'd find that mighty suspicious considering the circumstances. If he even has the right to refuse considering he's on probation.....
An indoor search of this magnitude is quite a violation of one's privacy. Even if innocent I can very much understand not wanting LE searching through every nook of one's home. How many people here would want the local police and FBI looking through your nightstand, closet and underwear drawers.