Is Virginia Woolf personally attached to Jacob Flender in some way?
There is nothing to suggest that Virginia Woolf ever knew or had a connection with a Jacob Flender. In fact, a web search of the name turns up primarily genealogical and census information. A search for Victoria Woolf and just the surname of "Flender" turns up little more. Since her death, some people by the name of Flender have written about her, but none of them a Jacob.
However, Woolf did write a story by the title of Jacob's Room, which is about the protagonist Jacob Flanders. We do not know Jacob Flanders to have been a real person, but the character and story may have been based on events Woolf experienced in her real life. The book is sort of an experiment in developing character. It does not follow chronology or what we might typically expect of a narrative of a person's life. For these reasons, it is all the more difficult to determine whether Jacob Flanders is based on a real person and who that might have been.
It is possible that the character of Jacob Flanders is based on Virginia's own brother, Thoby. Both the character and Thoby were educated at Cambridge and visited Greece during their lifetimes.