Does the Neoverse core have hyperthreading? I know that vCPU threads on the major cloud providers are hyperthreads instead of real hardware cores.
No, the Graviton and Graviton2 processors do not have SMT. Each vCPU (or logical processor, for a bare metal instance) is a core.
"Each vCPU is a thread of either an Intel Xeon core or an AMD EPYC core, except for A1 instances... Each vCPU on A1 instances is a core of an AWS Graviton Processor."