The Poké-BODY "Buffer" found on Hoppip, Skiploom, and Jumpluff should read, "If Hoppip/Skiploom/Jumpluff would be Knocked Out by damage from an opponent's attack, flip a coin...". So only attacks that do damage (not "place counters") would cause Buffer to be invoked.
Source: PUI Announcement (2005-04-05), PUI Rules Team (2005-04-07)

Relevant cards

Note: All applicable cards may not be listed below.
EX7_11
EX7_49
EX7_57