That depends on how fast they fail. A successful company should be around for years and will have lots of money to publicize itself; how long does it take the typical "failed" YC startup to fold?
Survivorship bias suggests failures are forgotten, and wins are remembered.
Watch out for big fraudulent companies though; they can do real damage.
The more unsuccessful companies YC has has the opposite effect and reduces YC's status as a kingmaker.
The bigger the batches the less close the relationships.