SmartThings is very capable of finding WiFi and LAN devices on a local network, as well as both querying status and receiving updates from the devices. Most tutorials do not include appropriate information on how to push status to the SmartThings hub as most of them include the IP and port in the device network id, but in order to receive push data it needs to be the MAC address.
Simple Lan Device Manager is a SmartThings smartapp which handles device discovery as well as updating IP information in case it changes.
Rest Switch is a simple device type that operates using JSON requests to query and change state.
WiFi Contact Sensor is a simple contact sensor device.
See devicetypes/README.md for installing Device Types, and smartapps/r3dey3/simple-lan-device-manager.src/README.md) for installing the SmartApp