It says something about SA's strength in depth that they can afford to have players of that quality on the margins. But I guess it's very similar to where NZ were with Carter and Evans. Eligibility aside, Snapper would have been snapped up by any team in the world except the one he was eligible for.
Louw and Esterhuizen are in a similar position. If they were EQP, I would even expect Eddie to pick them. Louw maybe offers less overall than Sinck at his absolute best, but I'd have him over the rest of the England THs today. And Andre is the kind of player England have been crying out for at 12 (and as an aside, is the kind of player that Matt Banahan could have been if he'd been consistently played at 12 - he only played there in a couple of matches but I thought it was so obviously the right position for him I was baffled he didn't play there more often).