Hi Henrique,
I tried to find out more by creating an instance in sa-east-1b and trying it myself. Worked like a charm. You seem to have all the bad luck 
I assume you had just created the instance? Are you logged in as root or as hdbadm? maybe you can try to run the command by logging in as root and running
zypper install gcc gcc-c++ gcc-fortran
(without the sudo), as sudo does not initialize a user's environment and maybe some environment variables are not set properly when sudo'ing from hdbadm - if that was too much admin talk, just ignore and run zypper as root.
good luck!
--juergen