Pirates were certainly familiar with Nova Scotia from the early 17th century onward. Peter Easton, a lesser known, but perhaps the most powerful and wealthiest pirate of all operated from his base in Newfoundland beginning in 1612. Easton sailed throughout the Atlantic and to the West Indies to ply his trade.
However, the candidate of choice by many pirate theorists is the famous Captain William Kidd. Before Kidd's arrest in Boston in 1699, he spent several years pirating the East Indies, and the Indian and China seas. Heading back to the West Indies laden with treasure, he supposedly steered his ship north before returning to port in Boston, which would ultimately lead to his conviction and death in 1701. Kidd's time spent in the north prior to his arrest in Boston left him ample time to conceal his treasure in the Money pit.
There is also the idea that more than one group of pirates used Oak Island as a communal pirate bank. Beginning in about 1625, and spanning into the 1700s, many buccaneers who were headquartered in Port Royal, Jamaica, including Sir Henry Morgan, Jean Levasseur, Bartholomew Sharp and others may have used the sheltered Oak Island as a collective treasure stash.
Of course, the problem with pirates is that they weren't known as the saving type... more so as spenders. Oak Island has always had a hint of military precision to it or at the very least, presents as a highly organized and disciplined undertaking. Pirates... you can't rule them out, but one might say it doesn't quite fit their profile.