Yeah they could. Anyone can play on any server of their choice.

Gunnlang is right, then there is just the Ping matter.. They will have to deal with a far worse ping than you because of their distance to the server.

realy depends what there ping will be.

use this to find there ping.

before the apac gets up in arms about possible poaching there are some Asian country's that get better ping to US then to Oz.

personally i am a aussie playing on NA-W but i know i will have issues with combat and such. so i going there for the friends and non combat based stuff.

sure i can be killed easy but i dont expect that to be a daily or easy thing unless i am stupid doing silly stuff. but any way just be aware they may have to give up on some game play options if the lag is to much.

how much is too much ? yet to be confirmed

You can play on any server that you want to no matter what. It is your choice to decide if ping is worth it. In some cases ping is better for some places on another server. But in the end it is not locational/ip locked for where you want to play.

Pretty much what everyone else said...you can play where you desire but ping may be a factor.

On that note: Voxelyria is a prealpha experience that is currently being developed and should begin it's rollout in the near future. Throughout Voxelyria, you will have the opportunity to test pings within the servers and their respective regions.