Sableye is a good tech period in a lot of decks. Disabling Blissey, Flygon d, Flygon ex d, Vire, and LOTS of other one attack wonders.
I reatreat Blissey all the time Prime. Holon WP is wonderful for that. I tend to use Warp Point with it too. It's nice to retreat for free, WP a benched pokemon active, and then KO it. Sableye wouldn't help too much against that. And as Jayson mentions Holon WP + water kills Sableye by itself ... and stops Dusknor, Gengar, and other damage counter dropping pokes to boot.
So how good a tech Sableye is depends on the Blissey build.