I'm not a Uniden user, so I can't really help you. You need to look at exactly which sites you're loading and activating in your scan configuration. Not all talkgroups are carried on all sites. I know that Town PD dispatch is one talkgroup that is typically carried on the Union site (must be Pacolet PD radios affiliating down there). But SCSO and SEMS are not carried on the Union site. Are you sure you're in receive range of the Spartanburg site? Manually program 853.700 and verify you can hear the control channel.
With zip code configuration you never know exactly what will be included and what won't be included.
Zip code 29031 is Carlisle, SC, which is on the far (south east side) if Union. It's very likely too far away to receive the Spartanburg site, and the Spartanburg site probably wouldn't be included in a zip code download, depending on if you set a radius.