[Edit: Since originally posting this article (from the Sunday Times newspaper) a number of stringers from the Wimbledon stringing room and other events have said that they have never seen anything that would suggest that pros use silicome spray on their strings. Whether that means that they spray themselves after the racquets have been strung or the article is BS no one knows. Nevertheless you should treat the article below with a healthy dose of scepticism since it does not quote anyone...
Pros using silcone spray on their strings
Pros using silcone spray on their strings