I don't tend to agree that Stokes was the proverbial "glue" that you're speaking of, but that's not to say that he isn't an important character, because he definitely was.
Barnabas was probably the most "central" glue-type character after his introduction, because the show was largely "The Adventures of Barnabas and Julia in Different Time Periods." Stokes didn't travel to every time period, although a person by the name of "Stokes" whether it Ben, or T.E. Stokes, was involved in many different time lines, but they didn't all have the same personality or vast knowledge of Prof. Stokes.
I would wager to argue that there were a band of these "glue" characters. By this I mean that there were a lot of them. Depending on which storyline you were in, you had a different character holding it together. For example, the early days of DS showed Vicki, and Liz to an extent, as being the central hub of the story. Once Barnabas was introduced, he became the central hub of much of the series until Quentin was introduced, during which time they went back to 1897 and many of the storylines based from Quentin.
So, it's not quite that easy to say that one character held the entire show together. Certainly one or two characters held each plot together, but the only character that held most of the series together was Barnabas. Now, as to whether or not that made him "important"....well, that's a much longer post than I'd care to type right now.