Assuming that the H atom density achieved is actually high enough for this to happen, it is considered unlikely for RM (which would then convert into UDH) to form without a surface that can act as a thermal sink for the condensation energy
Atomic Hydrogen is commonly recombined to molecular Hydrogen at the surface of the welding target by principle due to the relative lower temperatures near the plasma. This generates the extra heat that made AHW popular. Maybe this process prevails far above the process to form UDH. Gas pressure is relative high which probably also doesn´t help.