It is not "strictly forbidden" for audio but most time not recommended because you get low level output. But I use it since years in several cases whithout any problems to split the audio output to two amplifiers where quality is not the main issue.
In most cases for midi it works without problems because midi is very low speed digital signal. But avoid long cables!
Just try it! If it doesn't work for your equipment you loose just about 12 Euro (or something like this)