Let's say I have a incoming connection which is fixed 1Gb/s with tagged packets. And lets say that I need to connect that connection to a device which is a 10/100 device, which deals with the tagged packets.
Can I use a dumb (ie: non-VLAN-aware) 1Gb switch to connect that 1Gb connection and the 10/100 Mb device?
As long as the tagged packets do not exceed the supported MTU of the unmanaged switch, the tags should be propagated just fine.
Not all switches will pass this information. In the past, I have personally seen cheap netgear switches reset that portion of the frame back to 00's. This was a couple of years ago, but be aware that it's possible that your packets will be changed.
In my case the dumb switch is a Linksys EG008W. Linksys doesn't say anything about MTU, but this evaluation talks about testing the switch with jumbo frames and it works. So I would suspect this will work.