Is there any hard evidences for the bone case in Bosch season 1?

Could the police use them as evidence?

Not as direct evidence...no but rather as Circumstantial Evidence

Circumstantial evidence is evidence that relies on an inference to connect it to a conclusion of fact—like a fingerprint at the scene of a crime. By contrast, direct evidence supports the truth of an assertion directly—i.e., without need for any additional evidence or inference.

On its own, circumstantial evidence allows for more than one explanation. Different pieces of circumstantial evidence may be required, so that each corroborates the conclusions drawn from the others. Together, they may more strongly support one particular inference over another. An explanation involving circumstantial evidence becomes more likely once alternative explanations have been ruled out.

Circumstantial evidence is especially important in civil and criminal cases where direct evidence is lacking.

^Wikipedia

In this case, Bosch can show through testimony and photographs that Stokes knew Delacroix, was in possession of the victim's skateboard and lied about how he obtained it.

This may not be enough to convict Stokes but that's not the police's job.

At one point Bosch's partner says that the final resolution of the case is "a problem for the DA to sort out"..which it is.

All the police can do is arrest Stokes and leave the actual trial &/or conviction to the DA.