I'd support what Fella says, though I only mixed the two species briefly. I do keep both species in their own tanks though. Anyway, SAPs basically ignore anything but another SAP. They are sort of schooling fish, and while they don't form tight groups, they do follow one another about, and always rest together at night. As for irrubesco puffers, when I put the male in with the SAP, he showed a mild interest in the SAP, but the SAP didn't react at all to the irrubesco. They basically do totally different things: SAPs are open water fish, while irrubesco like to stay close to the undergrowth. Also, irrubesco are almost nocturnal, while SAPs are definitely daytime fishes.
So I'd say, probably worth trying. As with puffers generally though, individuals can be unpredictible, so have a Plan B just in case.
Cheers,
Neale