Based on my current research, enabling the unsecure DNS updates is a requirement for enabling DHCP Linux clients from registering their names with a FQDN.
While this works fine for Windows machines joined into the domain, the same doesn't work for Linux clients without enabling these unsecure updates.
As far as I know a machine would not be able to takeover another reserved name which would be the only real concern that I now.
Obviously it would be the DDOS but considering that we are talking about intranet here, I doubt this could be a real risk.
Do you have it enable on your domain or not?
Did you ever had to disable it due to having some problems with it?