GRIP isn't incompatible with USB cameras. You should try running the
v1.3-rc1 release, which fixes the problems that people have most commonly had with USB cameras in v1.2.
Also, if you're translating GRIP into code, OpenCV is easier than NI Vision, since most GRIP operations are just wrappers around OpenCV functions. We have a
reference table of what operations use what OpenCV functions, with links to to OpenCV documentation.