No, this is not supported. Only uplink interfaces. From the documentation:
You must interconnect EX3300 switches using uplink ports configured as Virtual Chassis ports (VCPs). Uplink ports 2 and 3 on an EX3300 switch are configured as VCPs by default. You do not have to configure these interfaces to connect EX3300 switches together in a Virtual Chassis.
http://www.juniper.net/documentation/en_US/junos13.2/topics/task/configuration/virtual-chassis-ex3300-cli.html
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