I believe you're referring to the arrow shard within the amulet given to Jolyne Cujoh in Part 6: Stone Ocean, rather than in Part 5: Vento Aureo, as this is the only time we see an amulet connected to the stand arrows in the series.
We are lead to believe that this shard works in exactly the same way as an in-tact one would, provided it can still break the skin of the recipient. We know this because it pierced Jolyne, Gwess, and Hermes - successfully creating Stone Free, Goo Goo Dolls, and Kiss, respectively.
For most people, getting pierced by a stand arrow causes them to fall sick, and later die. Others, however, may harbour the ability to habilitate a stand, and will gain one upon being pierced. We see this in Holy Kujo (Part 3: Stardust Crusaders) and in Josuke Higashikata (Part 4: Diamond is Unbreakable) when Enya Geil pierces DIO with a stand arrow, causing him to awaken The World. This causes many other members of the Joestar lineage to also awaken stands, however these two fall ill since they cannot withstand the toll it takes upon one's body to receive a stand. Therefore, if someone is punctured by an arrow shard, and they don't have the strength to gain a stand, it will eventually kill them in the same way that a whole arrow would.