Does Dacast support broadcasting via my own encoder?

Yes, Dacast supports almost all encoders which can output in RTMP or HLS.
This includes, but is not limited to, hardware devices such as:

TriCaster from NewTek
TouchStream from Digital Rapids
Cube from Teradek

This also includes software solutions as well, such as:

OBS Studio
Wirecast from Telestream
Discover Video
VidBlaster from CombiTech