There is some evidence that the Spurs FO use advanced stats to evaluate players. Those kind of stats show that Splitter is definitely a better overall player than Al Jefferson. Jefferson is about an average player and has been for most of his career.
I would think that Spurs would value Jefferson only if they thought he was a distinct upgrade defensively. And in any event they would not consider sending Splitter in a trade.
I think the Jazz should be able to get a better trade elsewhere.