Our Windows 2003 Server web server (my responsibility) is in another city and talks to a database server on our LAN (the LAN is someone else's responsibility) via a VPN. The VPN is established via a hardware firewall on each end. When the LAN Domain Controllers do their broadcasts, would the remote web server get them?
Domain Controllers don't do any broadcasts that are unique to Active Directory. Just standard ARPing, the occasion NetBIOS, and whatnot. If the VPN at both sites spans a single broadcast domain, then broadcast traffic will traverse the link, unless the VPN endpoints are explicitly configured to drop broadcast traffic.
This TechNet article breaks down all of the AD-specific services that need ports to be open between clients and DCs. As you can see, none of these protocols, other than NetBIOS, are broadcast-based and NetBIOS traffic happens on all Windows-based machines unless you explicitly turn it off.