Playing around a flag bearer
Unfortunately, neither of these spells will help you in this situation.

Vines of Vastwood, sadly, doesn't actually grant hexproof.  It appears to, as it has the same wording (and the latest Oracle text keeps this wording), but it doesn't actually give hexproof to the creature. This is an important distinction, because even if you play it on an opponent's creature, it doesn't prevent your spells or abilities, only those of your opponents, as worded.
(It really should be reworded to hexproof, but it hasn't been.)

Ranger's Guile is no use for a simpler reason: you can't cast it on the Standard Bearer, because it can only target a creature you control. Even the Standard Bearer's ability doesn't redirect Ranger's Guile; as the bearer isn't a legal target for the Guile, the ability never triggers.