Not necessarily. Just ask anybody who has messed around with the Credit Suisse line of ETF and ETN stock products. Just because something is backed by a commodity, it doesn't mean the owners of the asset will necessarily do a good job of making sure there is always a correlation between the asset and the commodity.

For your reference, I submit to you TVIX: supposed to move at 200% of the VIX or market volatility indicator but seldom does and frequently goes down when the VIX goes up. This is because its owners (Credit Suisse) have found a way to legally manipulate money out of people who are assuming this ETN (Exchange Traded Note) will correlate with the VIX, like Credit Suisse says its supposed to.