Ummm, depends on the letter, but those tend to be cut and paste "good, hard worker with brains and work ethic blah blah blah..." Without seeing the letter, I would say its not very helpful. While researching law schools and the process, I have come to realize just because a letter is from a powerful individual, doesn't make it a strong letter. If it reads very blah and very scripted, the school will see through it and it won't help that much.
I do believe that a good recomendation can help overcome lower numbers, but only to an extent. I wouldn't rely on that helping you overcome a 2.5, which is going to be hard to overcome, I won't sugar coat it for you. What schools were you looking at and what are you expecting (based on practice tests) for the LSAT?