Yes but you won't be able to bring your char from server to server. For example if you have a lvl60 char in US server, when you go to EU server you are empty

if your account use Malaysia address, you can only use RMAH in America region.

for second question, both game can be linked to same Bnet account.

Real Money Auction House, where you can sell or buy gears for your characters using real money.

you can only access one RMAH, depends on what server you're on.
there are 3 servers, America, Europe and Asia.
you can access GAH in all servers, but RMAH depends on your address.

and you can't change your Bnet address freely. you need legal proof that you live in that address if you want to change it like your IC.

note: GAH= Gold Auction House

last tiem selling in AUD really worth it
total 970AUD i got     

now still got pipu buy stuffs at RMAH meh?
i tot D3 economy went down the drain ady?