Yes, you can expand them live regardless of whether the ZVOL is a VMFS or RDM. Stopping VMs is not necessary but minimizing I/O is good practice (eg: do not actively be performing svMotion or snapshot consolidation)
Ensure that you rescan HBAs from the ESXi host after expanding the ZVOL and you should then see the new size. If you do not see the new drive size after a rescan, edit the ZVOL comment field from TrueNAS and save it, then rescan again.