Specifically you need
EA_HR 606 extension set
HCM_ESS_WDA_2 business function
Activated in trx SFW5 to get ESS Benefits functionality on WDA however...
If you are on a lower release should still be able to use Webdynpro JAVA Benefits in an EHP5 landscape - either unswitched or in a mixed UI - if you want some ESS services in WDA (with Benefits remaining on WDJ)
Hope this helps
