Haven't tried it but sounds like it should, it already have a few shell scripts for some captive portals.

"captive portal auto-login hook (configured via uci/LuCI), you are able to reference an external script for captive portal auto-logins (see example below)"

https://github.com/openwrt/packages/blob/master/net/travelma...

It can also auto join open networks "automatically add open uplinks to your wireless config, e.g. hotel captive portals (disabled by default)"