DT posited that Vito sent Luca off to meet with the Tattaglia Family "for no good reason." I think that there was a tactical reason as Vito rarely too any action without a purpose.
I think planting a mole was a great tactic, but Luca? I mean Sollozzo was so wily he knew Michael got the better of him within a second of his own death.
No way he and even Tatt Jr. did not see right through Luca. Just imagine if they strung Luca along and ordered him to do a hit on someone. Then what?