What would happen if I +1 Gideon, Ally of Zendikar turning him into a creature then activate Munda's Vanguard cohort ability with Vampire Envoy gaining 1 life from the vampire then putting a +1/+1 counter on each creature. What then happens to my Gideon both because of the ability and when he reverts back into a planeswalker
Gideon will be given a +1/+1 counter with Munda's Vanguard's ability, since he's now a creature even though he's also a planeswalker (C.R. 608.2i). The +1/+1 counter will remain on Gideon even if he stops being a creature.
Note that Gideon's first ability makes Gideon a creature in addition to his other types, because it says Gideon is "still a planeswalker" (C.R. 205.1b). See also this thread.
Note also that nothing in the rules says that noncreature permanents can't have +1/+1 counters (or any counters that modify power and toughness) on them merely because they're noncreature permanents (C.R. 122, especially C.R. 121.2 and 121.1a) — see Afiya Grove and Llanowar Reborn (C.R. 702.58a) for examples and see also this thread and this thread.
Note that Gideon's first ability makes Gideon a creature in addition to his other types, because it says Gideon is "still a planeswalker" (C.R. 205.1b). See also this thread.
Note also that nothing in the rules says that noncreature permanents can't have +1/+1 counters (or any counters that modify power and toughness) on them merely because they're noncreature permanents (C.R. 122, especially C.R. 121.2 and 121.1a) — see Afiya Grove and Llanowar Reborn (C.R. 702.58a) for examples and see also this thread and this thread.