Perhaps some day somebody will make a tool to play them back.
There actually are some tools, but I never got them to work.
Unfortunately the server-side demos don't record things sent to each client specifically (ie: various game messages, HUD, etc.) It just records the position of entities. The difference is that it isn't affected by the PVS system, so all entities get recorded, not just the ones within the view of the player recording the demo.