Yes, analog cameras can be connected as well, there just needs to be some device converting the video into a digital form which is supported by Angelcam. This means a remotely available stream using a h264 video encoding and RTSP streaming protocol or older MJPEG video encoding over HTTP.
Analog camera connected to a compatible DVR with h264 and RTSP support. In that case, you will be connecting to the DVR and the camera will be handled as one of its channels.
Analog camera connected to a video server (also called an encoder). The encoder will again need to support h264 and RTSP or MJPEG and you will be connecting the encoder. There are multi channel encoders available on the market as well, so in that case, you might need to specify the channel number representing the given camera.
Analog camera connected to an expansion card in your computer/server. The expansion card will handle the process of converting the video signal to a digital form. You will then need a software which will be able to act as a streaming server. For example, a VLC player can be used to do that. In this case, the computer will need to be running all the time when you want to have your camera streaming through Angelcam.