Not to my knowledge. Read the release notes for each version of code that can be run on a 4400 series controller. In the first couple of paragraphs the supported APs are listed. The most recent release notes for code train 220.127.116.11 supports these APs:
Cisco Aironet 1100, 1130, 1200, 1240, 1250, and 1300 Series Lightweight Access Points
In addition, the title of the most recent release notes for the 521 access point specify that it is an autonomous AP, indicating it would not be supported on a lightweight controller, and I doubt it is convertable to LWAPP.
Release Notes for Cisco 521 Wireless Express Autonomous Access Point for Cisco IOS Release 12.4(3g)JX1
The answer is no. The 521 is only compatible with the 526 Mobility controller. The full blown LWAPP controllers lack the MIBs for the 521 and if you attempt to attach it will fail leaving you an error similar to this "This AP is not supported on this controller". If you are looking for a low cost AP for the LWAPP solution try the AIR-LAP1131G-A-K9 at list price of $499.00. It is now orderable in the US. It is G only.