Probably not particularly wise - physical separation between DMZ and internal networks is probably more important than redundancy.
However, if you must do it, security is handled either:
- if you have a Layer3 switch doing inter-VLAN routing, using access lists on the VLAN interfaces
- if you have a firewall/router trunking VLANs to Layer2 switches, using the security features (including access lists) of the FW.