Think any of those players outsider Rapp will be starting this year? He should be considering his draft position. Or will they be brought along a bit slower?
The Rams do TEND to bring players along slowly, and exactly what will happen will depend on training camp, of course - not just how the draftees perform, but how others perform.
I think Rapp will be used in certain sets, but there are two starters ahead of him. He'll get significant playing time, though.
Long is targeted to be the third cornerback, though not necessarily in the slot but backing up Talib and Peters, so if the Rams have CB injuries again he'll get a lot of playing time, and at the very least will give them breaks. He should be a starter when one of the starters are allowed to sign elsewhere in 2020.
Gaines is the draftee most likely to be a starter, IMO. He'll be fighting with Sebastian Joseph-Day to be the nominal starter, though both will likely get playing time. SJD apparently has made a step up in the past season, but they drafted Gaines hoping he'd win the spot to be the two snap nose tackle. Some comments have been made that he should develop into an every down player.
Those are the defensive draftees who are likely to get many defensive snaps. Others should get special team time, some a lot of it.