Does a poisoned Fusion Strike Pokemon with Fusion Strike Energy attached take additional damage counters from Radiant Hisuian Sneasler's "Poison Peak" Ability?
No, because Poison Peak is an Ability and Fusion Strike Energy prevents all effects of your opponent's Pokemon's Abilities.
Source: TPCi Rules Team (2022-09-29)

Relevant cards

Note: All applicable cards may not be listed below.
SWSH11_123
SWSH11_123
SWSH8_244
SWSH8_244