I have another question. Was that area a part of Dwarka, or did Dwarka consist of just the island, but no mainland territories? One would have thought that although they were guaranteed a naval isolation, they'd have needed some hinterland in mainland Saurashtra to support the population of a city.
Anyway, regardless of whether Sudama came under (in this serial) Balarama's rule or not, wasn't it the duty at that time of any king to ensure that no citizen of his kingdom went hungry? And in those times, almost all kings, w/ some rare exceptions like Kansa, followed that. So wouldn't it have been the duty of the ruler of that place to see to it that none of his subjects - which would include Sudama - went hungry?
Another thing that struck me - if Sudama was Krishna's guru-bhai and so learned, Krishna could have taken his help as well by making him the guru of most of his sons (I know Pradhyumna was out of the question, but others would have been fine) or the family priest or something of that sort. Sudama could have been useful for even such religious activities, instead of just dwelling on Krishna, regardless of whether he was poverty stricken or floating on riches. Or he could have even been a kulguru to Parikshit (certainly better choice than Kripa) and the future Pandava generations.