What is the new vision of the creature? Does it retain its 120ft dark vision, or is that lost and replaced with 60ft darkvision of undead?
Unlike, say, the Shadow Creature template , Skeletal Champion doesn't modify the Senses category, so that remains unchanged. The Undead type says " An undead creature possesses the following traits (unless otherwise noted in a creature’s entry)... ...Darkvision 60 feet." Since a Skeletal Champion Drider would still have "Darkvision 120 feet" in it's entry, it retains that sense.
(A GM might strongly consider ignoring the CR calculation of Skeletal Champion, because, being based on the normal Skeleton CR calculation, it only takes Hit Dice into account and not the retained special attacks or special qualities - probably because normal Skeletons don't retain those the way the Skeletal Champion does. Since it keeps the web special, racial spell-likes, and 6th level casting from Sorcerer, Wizard, or Cleric; the Skeletal Champion Drider's CR should probably be higher than the normal Drider's.)