There is no way to check the load balancing on EX8200. You can just rely on 'show interface' counters to determine how much each interface is used.
For EX8200VC, keep in mind that local bias might get into action, changing the normal load balancing algorithm.
This is the KB showing which parameters are used for several EX platform for hash algorithm:
http://kb.juniper.net/InfoCenter/index?page=content&id=KB22943
And this one is describing the local bias:
http://kb.juniper.net/InfoCenter/index?page=content&id=KB22976
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If this worked for you please flag my post as an "Accepted Solution" so others can benefit. A kudo would be cool if you think I earned it.