Although there are more programs in soccer, track, and possibly other sports, I do not think those sports draw the following that lacrosse does. As evidenced by the poll results, people who follow lacrosse, really get into it. I know that there would be enough of a following in the two conferences that I follow most, CAC and ODAC, to have a great message board. There would be plenty of trash talk, game analysis, and recruiting talk to keep the boards really active.
One thing to note though is that I already know of one website that does give D3 lacrosse some recognition. Laxpower.com is an all around lacrosse site, that has a forum section with a DII/DIII message board. They get a pretty good amount of traffic during the season, but I don't think their boards are as easy to use as those used for basketball and football here on d3sports.com