You play viscera seer. It's not as good at dealing damage as tracker/conquistador. Sure, you can sac a creature that's being targeted to get to scry, but that's not worth taking up 4 cards in the main 60. Late game after a board wipe, you draw Seer. I, personally, would much rather have a creature that has potential to finish closing out the game in a couple turns rather than have a creature that, at best, is a chump block->Sac->Scry after a couple turns.
Those are some fair points and i would agree if you got your opponent to a low enough life total then Tracker/Conquistador will be better. I use Viscera Seer in combination with Bloodghast which works very nicely with [card]Cordial Vampire[/card} but that's the great thing about Vampires in general, there's multiple ways you can build them.
Pulse Tracker was one of the first one drop vampires i used alongside Stromkrik Noble but there's been better cards that we've got over the years, even Vicious Conquistador is a strict upgrade being a 1/2 so i can't see it really being that great unless your in a low to the ground aggro shell.
This is my current build in Mardu Colours primarily for Legion Lieutenant. I am very much interested in the new Sorin and also Knight of The Ebon Legion especially with a Aether Vial turn one can lead to some really nice three plays.
4 Viscera Seer
3 Cordial Vampire
4 Dark Confidant
4 Bloodghast
1 Captivating Vampire
4 Stromkirk Captain
4 Gifted Aetherborn
4 Legion Lieutenant
2 Vampire Nocturnus
Land
2 Godless Shrine
1 Urborg, Tomb of Yawgmoth
2 Mutavault
4 Marsh Flats
1 Mountain
2 Cavern of Souls
2 Blood Crypt
4 Bloodstained Mire
2 Swamp
4 Aether Vial
Instant
1 Terminate
1 Anguished Unmaking
4 Fatal Push
2 Fulminator Mage
4 Leyline of the Void
1 Engineered Explosives
1 Dismember
1 Wear // Tear
2 Kolaghan's Command
3 Inquisition of Kozilek
1 Collective Brutality