Well I wouldn't say all daycare workers are lazy or just want to do it only for the money, I know that isn't my intention. I do it because I didn't want to leave my son and after working with special needs children in behavior intervention, I figured childcare was the next best option. If I couldn't keep doing what I was doing before and loved, I can care for children and hopefully catch a few and help them before they get to the point of needing behavior intervetion anyway.
But back to the milk. Sounds like he is either getting just the right amount. I don't think you need a full 400 oz in the freezer and maybe just start cycling it out. Donate the oldest 200 oz and keep freezing any left over until you get back to 400 and keep doing the cycle. That way you know you have plenty on hand if you got sick or something or he did go through some odd growth spurt to where he did want more, but in general, I don't think most breast fed babies increase their intake that much more. And really, you might just find that he nurses more with you, rather then eating more at daycare. Anytime my daycare baby seems to go through a growth spurt he is on momma constantly, but he doesn't increase him intake for me.
I would also remind them though that it is their job to care for your child, not just feed him and they need to learn and figure out his cues.