So, GoPros are good for shooting action scenes?
It's the action camera category.
Believe it or not, despite the name action camera, no, they aren't. An action camera isn't designed for shooting action scenes, in fact, they can be a hindrance if not combined with other cameras. They're designed more for point of view sports footage (hence, action camera category), so keep that in mind.
When shooting action scenes, you change the focal length to help sell particular staple shots (punches, hits, swings, falls) found within action scenes. This is needed to be able to do many camera tricks and safely sell particular actions and stunts. This makes the usefulness of these action cameras limited when shooting action scenes. Combined with the Karma grip and the speed/ease of fluid movement shots, they're a great addition to the no budget action toolkit. It's not impossible to shoot an action scene with a GoPro, you just need to be aware of the options no longer available to you.
That is a good function for a secondary camera and used the DSLR for close-ups and control of depth of field shots?
Be careful. If I'm understanding you right, your plan is to shoot wide with the GoPro and CU with the DSLR. You may have difficulty matching the footage if you have a large focal length difference, not to mention you'll give your soundie a heart attack. Test before you go down this path.
Talk with your DOP. They'll be able to better explain all this to you than I can.