Are the Hoffman twins, Kara and Shelby, who played the baby in the movie, any relation to Dustin Hoffman? Why I ask is because he makes a small and rather pointless cameo in the movie, haha, so I was wondering if that's the reason for the cameo.

Nope.
Here's Dustin Hoffman's Bio that lists his kids.

Thanks CurlyBen... I did think it was a bit of a weird coincidence! But I guess Hoffman is a fairly common name.