Well, technically you could use the FS as a “proxy” for the network printer. Just to be clear, this would only work with a printer that has its own ethernet/wifi connection, and the FS would just offer an iOS compatible forwarding service.
After a bit of googling, I found that the steps to do this are:
Get CUPS on your Drobo (sorry, I don’t have it at DroboPorts)
Get Avahi on your Drobo (it is included with the FS firmware, but I’m not sure we can configure it to do this as well)
Configure CUPS to print to your network printer
Create a special Avahi config file to advertise the CUPS printer in an iOS compatible way
Here’s a starting point: http://www.micromux.com/2010/11/22/airprint-for-mac-on-linux/
You can also google for “airprint linux cups”.
In summary: yes, it should be possible, but as of now it’ll require quite a lot of work.[hr]
Hmm, actually, depending on the printer it may be a lot less work, and feasible right now. Disclaimer: This is pure speculation, so take it with a grain of salt.
It seems CUPS is only needed because iOS requires an Internet Printing Protocol (IPP) compliant server. In other words, if your network printer offers its services through an embedded IPP server, this should be almost too easy.
This other link offers a bit more details about the changes that have to be made in Avahi: http://www.finnie.org/2010/11/13/airprint-and-linux/
It seems that what is needed is just another file in the Avahi configuration folder to tell iOS devices about the printer. See step 6 of the previous link for a template for the configuration file.