There are three things here:
1. Does the DHCP server hand out IP addresses that are configured in DNS?
It may, and it may not. The DHCP server on my home network, for example, gives out addresses which it also provides DNS answers for. At work, the DHCP server and DNS servers are completely separate, but the DNS server is populated from a database that knows about the systems registered to use DHCP.
2. Are the DNS addresses given out to your system "real" public DNS records?
In my case at home, no, they're not -- they're invalid .local addresses. They work because my internal systems are resolving addresses using my DHCP/DNS box, which has been configured to answer queries from my internal network. Even if I opened that box up to the world, no one else would know to look at it to get an answer for "laptop.local", because the root servers don't know about it.
3. And finally, are the IP addresses given out public addresses rather than 10.x.x.x or 192.168.x.x (or other) private-range addresses? And, (point 3½) if they are public, is there a network firewall which protects the system from external access?
In the example of my home network, they're private addresses. At work, we're migrating to private addresses, but some systems are given NAT access through the firewall. (This isn't the default and needs to be justified and configured on a per-system basis.)