This article discussess iCloud security: http://support.apple.com/kb/ht4865, but the primary issue you'll run into sharing a single account is that when you do this, everyone's synced data is merged, and the merged data appears on everyone's device(s). Also, any action on one device is replicated to all other device. If, for example, one person deletes a contact on their device, it is then deleted from all other devices sharing the account. You would end up seeing, for example, each other's contacts, calendars, email, etc. Each iCloud account also comes with a single iCloud email account and 5GB of free storage, up to a maximum of 55GB with purchased upgrades. With a number of people sharing the account you would quickly run out of space and may not be able to purchase enough to accomodate everyone.
Furthermore, iCloud is designed for personal rather than business use. As such there are limits imposed on services like email that may not be sufficient for a business environment (see http://support.apple.com/kb/ht4863 and http://support.apple.com/kb/HT4489).