well according to the comic vegeta did say that they all were super sayians. and If raditiz is currently stronger than frieza and all his elites, Then its not out of the realm of possibility that kakarotto could have become a super saiyan at least
And now they showed universe 13 Kakarotto transforming, so it's confirmed. Panda, in case you have no clue what we're talking about, it's the webcomic DB Multiverse, which you should read. Pretty awesome.