In general, pretty good condition. The ORUs are designed to live outside for their functional life (more less the same as station's), so there's generally no reason they can't live outside while they're waiting to be called upon. Many of them have flight support equipment (FSE) that provides some support to keep them alive. These are typically heaters, sometimes telemetry monitors.
They are evaluated for environmental risks just the same as the operational ORUs are -- most of them are better protected in their stored locations, by virtue of the location itself or by dedicated covers. Both of these options generally serve to create a more benign environment for the ORU than it would experience in its deployed, operational state.
Not all spare ORUs are stored outside. Some are small enough (the Sequential Shunt Unit, for example) to be kept indoors and transition through the airlock with the crew. There's a trade-off to be made, however. Keeping an ORU outside presents the opportunity to be able to replace it purely robotically, if it was designed with that in mind.