You can disable Smart Card login for iDRAC in two ways
1: Using Local Racadm
Install OMSA on the server and run following local racadm command to disable Smart Card Login
racadm config -g cfgSmartCard -o cfgSmartCardLogonEnable 0
2: Using iDRAC6 Configuration Utility
a) Turn on or restart the server by pressing the power button on the front of the server.
b) When you see the Press <Ctrl-E> for Remote Access Setup within 5 sec..... message, immediately press <Ctrl><E>.
c) In iDRAC6 Configuration Utility, you can disabled Smart Card Authentication