the primary wesm will work all by itself...
the redundant wesm can be configured in 1 of 2 modes to work with the active wesm:
1) stanby-active mode - be a standby and come alive using the config and RP licenses of the primary wesm
2) active-active mode - where the redundant wesm can use 1/2 of the primary's RP licenses and actively adopt RP's, and support full working operation with the primary also working at 1/2 load
hth...jeff