Seeking is supported tho, as are audio-only files.
How would you expect the video bits to get from the machine running VLC to the chromecast if the network drops? Not sure what you mean by "regular chromecast", but if the network connection between the chromecast and the video source is lost, you lose playback. That's true if you're watching YouTube videos or Netflix, or if you're using any other app to cast something from your local network.
Speaking of which, the casting with VLC also has major buffering problems. Even casting a low-def video directly from an SSD to a Chromecast Ultra (over ethernet!) it will buffer for about 1-2 minutes for every 5 seconds of playback.
VLC could do that for network sources. Even for a local file source, it could copy the whole file over - the Chromecast has a decent amount of RAM.