Saints were interested in Harty at the end of last season, but he decided to go to Hamilton instead. However, he never played for our first division rivals and was transfer listed after a breach of club discipline regarding the medical staff. He was also reported to have gone AWOL.
I'd imagine there isn't much truth in this rumour, especially as Harty was released by Hamilton after the transfer window shut, thus meaning he couldn't be signed until the summer at the earliest. When fit he is a decent striker and scored lots of goals with Clyde, but Saints probably wouldn't want to take a risk on an injury prone player with a discipline problem.
Story source: The Sunday Mail