If they really wanted to then YES.
Tracking website traffic from your router allows you to see a complete breakdown of the sites that have been accessed through your network. Routers track traffic using router logs, which list the data packets that have entered and left the network through that router. This type of tracking can be a useful way of monitoring your Internet usage.
Router Logging
Logging capabilities are usually part of a router's firewall function. Firewalls provide a network security service that examines all network traffic as it enters or leaves a network. With logging enabled, the router takes a record of all firewall activity and stores it in a text or Comma Separated Values file. You can then use these router logs to work out which sites have been visited from your network by looking at the outbound packets that have passed through the firewall.
Disadvantages of Router Logs
One disadvantage to tracking Internet use through router logs is that the logs themselves often require a degree of skill to interpret. For example, it might not be immediately obvious which packets are outbound packets and which are inbound packets, and most logs only list IP addresses instead of human-friendly Universal Resource Locator links. In addition, checking raw router logs does not give you any indication of which user attempted to access a given site.
Log Analyzer Software
Log analysis software, such as WallWatcher and Link Logger, helps you to work around some of the disadvantages of using router logs. These programs take logs straight from your router and process them into a more readable format. In addition, most log analyzers are able to store usage details and compile statistics over a period of time. This can help you to identify whether a few particular sites are being regularly accessed through your network.
Your ability to monitor the sites accessed by your Wi-Fi clients depends on your networking hardware. The easiest way is to download a network monitoring software that uses Simple Network Messaging Protocol. SNMP, however, is not supported on most home routers. Even with SNMP, the information is not always detailed enough to identify specifically who is accessing which site. A more thorough option involves port monitoring. Business-class wireless access points often include a port monitor option to connect a wired PC directly to the access point through Ethernet and have all wireless information forwarded to you. You can then use a sniffer to identify which IP addresses are making Internet requests to which servers; however, sniffers can only evaluate non-encrypted data. If the user you’re monitoring is connecting through a VPN tunnel, for example, you’ll only be able to see the endpoint address of that tunnel. Alternatively, you can invest in hardware-based Web monitor, which is then wired in-line between the Wi-Fi router and the Internet modem. This approach may be too expensive for the average user, however.
I suspect though that the person who sets up the hall wifi will have the same qualifications as the person manning the microphones..