I have a Go pro 3 hero with a USB connector .. no Mic IN.. but there seem to be a adapter to a mini jack input.
I will order that adapter and see how it goes. I will not use your splitter trick .. the splitter is made for audio OUT . when you use it as a combined audio IN connector its just a matter of time before 1 of the 2 sources will burn out .. I am an Audio technician and this is something i would not advise.
better use the audio in from the drum module and the main out from the module to the recording device.
I should correct my prior post, the connections go as follows: from my ipad to the aux in on the module, from the headphones out of the module to a splitter, one side goes to my headphones, the other into the mic in on the go pro, which is NOT going to cause any damage to anything. sorry if I created confusion. but the other option is to just get a small behringer mixer and combine the two inputs and use the headphone out from there, your sound quality will suffer, ( I have one and I tried it that way there is a very noticeable difference), I also have a Focusrite sound card, that works fine but you need to involve a computer (laptop in my case) in order to use it. there are multiple ways to record, I just provided the simplest one. the best way is to record from the module out to a sound card and add the audio to your video later, you get the best quality that way, but you have to sync video and audio which can be a pain, by connecting the GoPro directly to your audio source, you don't have to sync, it will be already done, the only thing you have to do is to edit beginning and end of the video to remove any unwanted parts.