How do the equipment restrictions put on a character
by the Vow of Poverty feat affect class-defining items?
(Examples include a cleric’s holy symbol, a wizard’s
familiar, a samurai’s daisho, and a paladin’s mount.)
The Vow of Poverty feat is very specific about the items
that a character can own while gaining the benefits of the feat
(BE 48). It specifically disallows ownership of masterwork or
magic weapons, and thus a samurai who chooses this feat must
give up the possession of his daisho (his pair of masterwork
weapons).
A holy symbol does not appear on the list of eligible
items, and thus a strict reading of the feat would disallow the
item.
A familiar, special mount, or animal companion isn’t a
material possession, and thus a character with Vow of Poverty
isn’t restricted from gaining the benefits of such creatures.
Remember that the Vow of Poverty feat, like most of the
material found in BE, is intended for mature campaigns that are
capable of handling difficult role-playing issues—it’s not
intended for most hack-and-slash games. A cleric who must
give up his holy symbol (effectively preventing him from
turning undead or casting any spell that requires a divine focus)
could be a very interesting challenge for a player who’s “done
it all” and wants to try something unusual.[/b]
And while the intent of the feat and book itself is contradictory the RAW is that a holy symbol is not allowed - but you can borrow one
Pg 20
"One option is for ascetic characters to beg components from other party members, who are probably gainng as much benefit from having the spell cast as the caster is."
So as the Sage pointed out a "strict" reading of the feat dissallows use of a holy symbol (well at least ownership of one).