Yes, the have an ipad by reception that you book and pay and it will come by in the morning for you. Domestic Terminal is walkeable if do not have much luggage. Need it for International
Just a clarification: If you're going out of the domestic terminal, it indeed is an easy walk. The signage leaves a bit to be desired, but the information desk in the airport apparently gets asked about six times an hour how to walk to Ibis. The directions above get you back.
If you're staying at Ibis for an international departure, it's not an easy walk. In that case, you do need to arrange the ride in advance. There's a computer terminal on the registration desk at Ibis and for $5 you can pre-purchase your ticket. The driver doesn't accept cash and if the coach is sold out, they won't let you on, so booking in advance is a good idea. Note that although it's fairly close, it takes a bit of time as there are a bunch of one-way roads and the coach stops at the domestic terminal before it goes to the international one. We were about 20 minutes on the coach for what looked like a 2km ride.
I believe you can get tickets when you arrive. However, if you are only going to the IBIS it only took me 10 minutes to walk there with my case. Just turn left when you come out of the domestic terminal and you will see it in the distance. Walk along the footpath until you are opposite the hotel and then you can cross over the road straight into the IBIS.
Get an answer from Ibis Brisbane Airport staff and past guests.