The issue the cameras bring to the table is just the port forwarding.
Normally with this type of set up, port forwarding is enabled on the router to forward traffic on the specified port to the camera or DVR. Very simple to do. However if you use 2 NIC's on the SBS and you do not use ISA, you should have a router between it and the Internet (IMHO). Once you do, you then have to forward traffic from the router to the SBS, on the SBS configure port forwarding to the specified device (not a simple task), and configure the firewall. It also adds some additional traffic on the server. Using a single NIC again makes this very simple. Traffic can then be simply forwarded from the router to the camera/DVR as it would normally be done..
DHCP and DNS are totaly different issues. DNS MUST be handled by the SBS, and DHCP should be handled by the SBS. Doing so does not complicate matters in any way, improves performance, and adds some advantages.
I have attached a sketch of the physical configuration.
If you like we can chat, but keep in mind Experts -Exchange requests that the bulk of the discussions remain here to assist others as to the solutions found.
If you wish to contact me directly use the e-mail address on my profile (click on RobWill). I too am in Canada -East Coast)