Yes, but some folks are wary of using the same physical port for external and internal traffic. Fears of "VLAN hopping" remain, even if unfounded. Also, you'll hit a performance wall since you are sharing a single gigabit port between external and internal traffic. Obviously may not be an issue for many, but if you have gigabit fiber...
I have gigabit fiber and none of this is an issue.
VLAN hopping is only possible due to misconfiguration. I'd like to be proven otherwise if that's not the case. VLANs are used EVERYWHERE where it matters. And no, the single port is absolutely not a bottleneck because the port is full-duplex.