Basics of ID'ing camshafts.
 Roller vs. flat tappet
Telling one from the other visually is relatively easy. The roller cam will have much more rounded lobes, like the big end of an egg. A flat tappet cam will be much more pointed, similar to the small end of an egg.
In the image on the left is a hydraulic roller cam, the rounded lobes are readily appearant compared to the flat tappet cam to the right of it.
Often roller cams will be made of steel and will be shiny instead of a flat black/gray color of a flat tappet cam caused by the anti-wear treatment it is given.
 OEM SBC roller cam
A cam made for use in a SBC that originally came with a hydraulic roller cam will have a step machined into the nose of the cam for the retainer plate.
A cam without a step could still be a hydraulic (or solid) roller cam and it could still possibly be used in a late roller block by using a cam button to set the cam endplay instead of the factory thrust plate. The maximum lobe lift allowed is about 0.354" before the factory hydraulic roller lifters can lose contact with their retainers (aka "dogbones"). Aftermarket lifters are available that are longer and prevent this from happening.
A factory-type hydraulic roller cam can also be used in an earlier block by using a spacer to take up the room the retainer uses, along with a cut down cam button. The spacer can be made by removing the ears off of a stock retainer plate, or a kit can be bought from Lingenfelter that has the spacer and special cam button included.
Roller cams cannot use flat tappet lifters, and vice versa. Besides the possible mechanical interference between a flat tappet and a roller cam lobe, the timing events will be skewed much to badly for this to work. A roller lifter on a flat tappet lobe would have very little duration, a flat tappet on a roller lobe would have way too much duration, even if it could work without mechanical interference.