Okay guys I really have a few questions. My first is will smallmouth and other River bass eat small bream that are 2-4 inches? And next question is will I catch a descent amount of bass using minnows/small bream/baitfish? I have a net so that I can get all. I am fishing in a rocky river with clear water at 1-6ft. I'm not looking for size. Btw I can get 3+ minnows with one swipe with my net. 

Smallmouth eat anything that move.

They will eat whatever fits in their mouth and try stuff they can't depending on their mood. Try any of that under a float with a few feet of line to let the fish swim and you should catch something. I like hooking bluegill in the back right under the dorsal and letting them swim like this in ponds and lakes for flatheads, stripers, and largemouth. Some people frown on live bait but I go fishing to catch fish

This last weekend I has to separate a smallie that was about 12" with about an 8" perch stuck in its mouth floating on top of the water. 

The smallie swam off, the perch didn't make it. RIP little buddy. 

This one had a big crappie tail sticking out of it's throat and still tried to eat my crankbait.

I have a friend stocking a lake for smallmouth and the fisheries biologist said that smallmouth bass don't do well with bluegill as they won't eat them often enough to control the population. They are stocking rock bass and crappie instead.

bagofdonuts, the smallies in that lake are epicures.  In my river, the South Branch of the Potomac they will attack anything that moves and looks moderately yummy. 

Smallmouth will indeed take advantage of an easy meal given the opportunity.  Most predatory fish will.  However, studies have shown that in some cases, up to 80% of their diet may be crayfish or gobies if they are present in the system.

Smallmouth will basically eat anything that either seems like a viable food source or is smaller than them and irritates them.  That said, they have distinct preferences.  If I'm picking bait on a river or stream, I'm looking for helgramites or madtoms first, followed by gobies/sculpins probably next, Shad/alewives (if present and legal), perch, crayfish, and then eventually sunfish and crappie.  Most folks I know using sunfish for bait target catfish.

I used to live-line small bluegill in Champlain for mega smallies. 

I've caught many smallies over the years on crankbaits and spinnerbaits with them having bream/bluegill half way down their throats. Smallies are aggressive feeders.

I caught a 2.5 lb smallmouth fishing with a hand sized bluegill for Striper once 

This past week every clump of grass we went by was packed with inch long bluegills, and coincidentally, the smallies were cruising the grass edges. Several of them spit up bluegill as we were fighting them. 

Blue, nice fish. Love the gut on that pig.

I know the smallmouth in the river I fish will eat anything they can get in their mouths. They seem to prefer crawfish and smaller shiners but they are pretty versatile in what they can and will eat.