Be aware of the broadcast flag, see RFC2131 (page 24):
A client that cannot receive unicast IP datagrams until its protocol software has been configured with an IP address SHOULD set the BROADCAST bit in the 'flags' field to 1 in any DHCPDISCOVER or DHCPREQUEST messages that client sends. The BROADCAST bit will provide a hint to the DHCP server and BOOTP relay agent to broadcast any messages to the client on the client's subnet.
EDIT
A client that can receive unicast IP datagrams before its protocol software has been configured SHOULD clear the BROADCAST bit to 0. The BOOTP clarifications document discusses the ramifications of the use of the BROADCAST bit.
Added the rest of the RFC. According to the entire paragraph, it could be either broadcast, or unicast or even both.
