Of course you can as long as you use a unique address not already in use. If using DHCP and static addresses, limit the scope of DHCP to the number of dynamic devices you expect to use now and in the future, then assign static IPs to the other devices using addresses outside the scope.
For example, Airports tend to use 192.168.1.1 for the default router LAN address, and use a Class C 255.255.255.0 subnet mask. This allows for up to ~255 unique addresses on the subnet. Obviously if the router uses .1, then anything .2 to .254 is fair game for hosts on the private LAN side. .255 is typically a broadcast address, meaning it is sent to all hosts.
So, for your DHCP Scope for example, set .100 to .250 for client addresses then use .2 to .99 for static hosts. Make sure you use the correct subnet mask, default router, and DNS settings on static hosts, these are things DHCP does automatically for you. You should keep track of static addresses you use in a spreadsheet or similar so you know what is already being used.
All that said, there are few situations where static IP are really necessary.
DHCP servers including airports allow reservations. By adding an entry for devices you always want to keep a particular address, enter the MAC address (12 Hex characters with : separators typically) and IP address for each "static" device. Now, the clients will send a DHCP request when they boot up, and the router will recognize the MAC address and return the "Reserved" IP address for that device. It still provides all the other configuration parameters like any DHCP device, the only difference is it always supplies the reserved address for these devices. Now, no messing with setting static IP on each device.
Finally, the nature of DHCP is the devices tend to retain their addresses, and you can make that even more possible by setting a high DHCP lease time. By default, it is probably something like 7-14 days, and you can set it higher, like 99 days I think, maybe more. How does this help? A Lease time means the router won't assign the address to another device until after the lease expires. Assuming no reboots, when the half-life of the lease is reached, the host sends a DHCP renewal request to the DHCP server. If the server (router) is up, it acknowledges and resets the lease expiration date for the number of days set in the lease time setting. If the router is down, the host keeps trying to renew its lease.
As long as the network, or any device is not down for 2X the time of the lease, it will get the last address it had previously again. 2X is because the DHCP server won't assign a previously used address for twice the number of days after a lease expires. So, you see, even DHCP attempts to keep addresses somewhat static, without forcing you to manually configure the network settings on each device.
The longer lease times are fine on most home networks, you are nowhere near the limit of available addresses. But ISP leases are often shorter, because they tend to use most of the addresses in each scope and want them to be available as soon as possible if your network stays down for a long period. So, they may set lease periods for two days for example.
I only use static on servers at work in my labs. At home, I use reservations to make things easier to manage. And, I use longer leases. Even my DHCP client hosts retain their addresses for years, surviving 1-2 day power outages even. So, all this to say, static IP is generally more hassle than necessary for home networks.
Aren't you glad you asked (sorry for the long reply, hopefully this will be helpful).
