Gum paste powder is regularly mentioned on these forums, but I haven't been able to find it in South Africa. What I do find is arabic gum powder.
Does anybody know if this is the same thing?
Yes it is! Just add it to your fondant to make gumpaste!
No, gum arabic doesn't act the same way as the other gums used to create gum paste. I don't recommend using it. It can be used to make a decent gum glue, however, to glue pieces together.
Gum paste powder--like that made by Wilton--will have CMC (Sodium Carboxymethyl Cellulose Gum), tylose, or gum tex, or gum tragacanth added to it. You can get those powders by themselves and add them to ready to roll sugarpaste and create gum paste.