VLAN security and 8021q.o ???

My question deals with how secure is VLAN and Linux? I have noticed that Suse compiles 8021q.o as a module. I have experimented with it and works quite well. Is there any security issues for say .... connecting a secure network through VLAN 5 and and insecure network through VLAN 6 to a server through 1 NIC. And suppose the server is one of those newer nifty 1U servers that do not provide many PCI slots for multiple NICs. Thanks for any input, Craig Herring