Yes, the 8 SP 3 version of EV comes with a new add-in. No it won't cause any problems if you use the existing 8 SP 2 addin.
The most noticable change in 8 SP 3 client (which requires 8 SP 3 server too) is virtual vault.
You can look at more details from this page :
http://seer.entsupport.symantec.com/docs/308967.htm
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