I'm sorry, I can't give you any opinion on the questions you ask, but I think I can give you some background on pros and cons. I haven't used either of the programs you are wondering about, but I have used a program that was stand alone and one that was integrated and I will give you of what I think are pros and cons.
I have used Gibbscam and I have used Pro/E with the Pro/Manufacturing CAM module. Gibbscam is standalone and Pro/Manufacturing is made by PTC and integrated into Pro/E. Holes are one of the biggest problems in CAM files. In a stand alone program you can't tell if a hole is tapped or through or a pipe tap or a reemed hole. When you pass a part from a CAD package to a CAM package, that info doesn't come through. So if you are trying not to make a drawing, that is difficult to do in a stand alone program. With Gibbscam there is a hole manager that can "read" what type of hole it is based on a hole diameter. If you have a unique hole diameter set up from every type of hole, it can automate drilling and tapping.
Pro/Manufacturning was also supposed to be able to be more seamless because when the model updates, the CAM file will update too. Well, Pro/Manufacturing could only handle very minor changes before it required a do over, so I kind of throw the plus out of the equation for the integrated part. You may want to let your programmers have a glimpse of each program. Pro/Manufacturing and Gibbscam both were CAM products, but it was very easy to see that Gibbscam was designed by people that understand machining, and Pro/Manufacturing was designed by a CAD company.
So you might want to find out what the link is between the cad program and the cam program. Find out how each program handles holes. And I know you don't want to complicate things further, but if you haven't gotten a visit from your local Gibbscam rep for a demo you really really should. That program just works. There is so much control and yet it is very easy to use and powerful. Their tagline is "Powerfully Simple, Simply Powerful" and they aren't telling you any lies.