BusyCal can sync with iCloud and over a LAN simultaneously.
You can publish iCloud calendars on your LAN for others to subscribe to. iCloud will only sync calendars that are hosted on iCloud. So, if Fred wants to sync calendars over the LAN with Mary while also syncing those calendars with iCloud, then the calendars must be hosted on Fred's iCloud account and republished over the LAN for Mary to subscribe to, like this:
If both Fred and Mary are syncing with iCloud, then they should share calendars with each other through iCloud rather than over the LAN.
If you need to share calendars in a workgroup where some users use iCloud and some do not, you can setup a hybrid workflow where the iCloud users share calendars through iCloud, and the non-iCloud users sync over the LAN.
You can set up one of the Macs on your LAN as a server that republishes the iCloud calendars over the LAN for non-iCloud users to subscribe to.
In this example, the LAN server is syncing with the widgetco@me.com iCloud account and republishing the iCloud calendars over the LAN for the non-iCloud clients to subscribe to. Those who have iCloud accounts (dave@me.com and mary@me.com), are not syncing over the LAN. Instead, they are sharing calendars with each other through iCloud.