Are you using Domain Mode or Standalone Mode of EAP6 ?
Also are you facing this issue only with a particular version of Informix driver or did you test with some other drivers as well?
Just to isolate the actual issue can you please let us know if you are not able to list the installed drivers in the EAP6 management console ? Or the following kind of CLI command is also not able to list the installed JDBC Drivers?
As there is some issue reported with the Management Console for not listing the installed JDBC Drivers properly like :