Hi Mike, and welcome to the WXForum,
Similar questions have come up over on the WeatherCat forum, although related to personal Macs, and not servers. According to the developer, the Mac OS is the cupric, not the weather application. If an individual is not logged in, a process can not happen in the background. The case I remember was a shared family computer where the husband, wife , and kid(s) each had their own login and used fast-switching to change accounts. The account that WeatherCat was running on had to be the logged in account to receive data from the weather station and send data to a web site.
Now, I don't know if this applies to a server account that is not logged in, but I would suspect it is the case. Pop over to the WeatherCat forum and ask WCDev, as he's active daily (although in the UK, so timing may be delayed a bit.)
http://athena.trixology.com/index.phpSteve