I don't think that's possible. But just out of curiosity, why do they need to login into iCloud? As you are probably aware, you walk a thin line by making that option available as the iPad may not get past the activation screen if the iPad is reset and they have enabled Find My iPad. You'd need to go to an Apple Store with proof of purchase, company letterhead stating you are authorized to get the device unlocked, and some identification. Not fun....

Once they are logged in with Find my iPad turned off, you could push a profile with 'Allow modifying account settings' unchecked, but it'll also disable other logins..

If devices are Supervised, Actication Lock does not turn on if Find My iPhone/iPad is enabled.

I have several supervised iPads that have Find My iPad turned on and the activation lock is enabled. I believe this is a default setting. If yours are disabled there must be a setting you have turned off or active to keep the activation lock from happening. I would really love to know what this is.