It is possible to run WEP and also have other SSIDs using different forms of authentication.
As I am sure you know, WEP is extremely insecure so be mindful of this while using these devices. If there is any type of sensitive information, I would recommend the customer move to a non-legacy protocol.
ADTRAN Product Support Engineer.
Completely understood. The customer had scanners that on their previous wireless system, worked perfectly fine but ran WEP. They wanted to use WPA/AES (which I am not even sure is possible. I thought it was either WPA2/AES or WPA/TKIP) and was having rough issues with the scanners, but not mobile devices. We had to revert down to WEP yet again to test stability of the scanners. During a packet capture, I would notice the AP deauth'ing the scanner due to an error code 11, invalid element. The scanners were very instable which is the cause for the change but we are aware of the WEP issue and the customer was made aware of it as well.
Also be aware that WEP is broken in V2.8 and later. It does not require any authentication at all.