Sollozzo welcomed Tom's discovery of his association with the Tattaglia's. That assured him that noone had discovered his alliance with Barzini.
I was always puzzled by Sol's "My compliments" to Tom after Vito asked about the percentage for the Tattaglias. It would be in Sol's favor for Vito to know that the Tats were backing him so Vito wouldn't think he was some two-bit punk (as Woltz would put it). I doubt Vito would have sanctioned the meeting if he didn't know that Sol was backed by another Don. And, as you point out, it helped hide Barzini's role.
