MacTCP does not support the DHCP protocol. Most DHCP servers can support BootP protocol simultaneously. MacTCP used in server mode can work with a BootP server. The Open Transport networking architecture includes a TCP/IP protocol stack that supports DHCP.
MacTCP's dynamic addressing is analagous to AppleTalk's dynamic addressing scheme. When the machine boots, it picks a random IP address and then checks the network to see if another machine has that address. When MacTCP was written, DHCP did not exist. It has since become an industry-standard, so Apple has dropped support for its proprietary dynamic-addressing scheme in favor of the industry standard DHCP.