I don't know how good of a caddie he was, but if he put the commitment and intensity into helping his player(s) like he did everything else...Seve would have been an ace!
A great article from the archives, by Peter Dobereiner on Seve's early days, from a Golf Digest issue published in 1980, well is worth reading for insights into his early years and development. It's titled, "The Enigma of Seve Ballesteros."
Again, yet another example of what the game stands to lose as it continues to turn its back on better supporting caddie golf! How many youths did he spur on to take up the game. How many millions did he entertain? The greatest shotmaker of the modern era...a man from humble origins...a caddie at his core!!!