Lightningrod is never a good ability for a Rhyperior, and I'll tell you why.And Rhyperior but i guess he will be overshadowed by his other ability ?
1: With or without the ability, Rhyperior, as a Ground-type, is already immune to Electric moves.
2: Due to its natural immunity to Electric moves, Rhyperior cannot reap the Special Attack boost from Lightningrod.
3: Even if it could have its Special Attack boosted by Lightningrod, its Special Attack is so low that it wouldn't matter in the slightest.
4: Solid Rock exists.