What is "Otzar Hashem"?
Radak: It is the Ohel Mo'ed. The Hekdesh from the spoils of Midyan, i.e. the gold that the officers (appointed over 1000 and 100) gave (Bamidbar 31:48,50).
Does Cherem go to "Otzar Hashem"?
Malbim: What is not proper for Otzar Hashem is Cherem. Gold and silver, which are proper for Hekdesh 1 , go to Otzar Hashem.