Can I use grpcurl against the sandbox ledger API?

It needs to support the reflection service for this to work without supplying proto files. Does it support this?

Yes the reflection service is active and you can use grpcurl with the ledger api, e.g.

grpcurl -plaintext localhost:6865 com.daml.ledger.api.v1.LedgerIdentityService/GetLedgerIdentity

Keep in mind that as of SDK 1.0.0 we switched the namespace for the services from com.digitalasset to com.daml. And while we added “proxy” services to still support the pre 1.0.0 namespace, the reflection service doesn’t properly pick this up, and therefore you grpcurl only works with the non-deprecated com.daml namespace of the service names.