So my question is pretty straight forward, I have a GPS module (link below) with the given antenna for it which is perfect for that module (also linked below).
My pondering make me wonder if I can also share this antenna with a HC12 serial module that uses 433MHz with 100 channels (perhaps one of those channels for the best results).

I had hopes for it to work considering the serial module is roughly a third of the GPS frequency (GPS operates at 1575.42 MHz and 1227.60 MHz).
I am a student and did take emag classes but we never really covered this

I guess if there is no straight answer, would it do any harm to connect two antenna ports with a Y cable? any back feeding issues foreseen?

Links:
https://www.adafruit.com/product/746
https://www.adafruit.com/products/960
http://www.seeedstudio.com/wiki/images/b/b0/HC-12_User_Manual.pdf

 

I wouldn't expect it to work particularly well. As long as you don't key up a transmitter into an open receiver you can experiment. If you do have a transmitter and a receiver on the same antenna you need a duplexer to prevent the transmitter from frying the receiver frontend.

 

My pondering make me wonder if I can also share this antenna with a HC12 serial module that uses 433MHz with 100 channels (perhaps one of those channels for the best results).

I had hopes for it to work considering the serial module is roughly a third of the GPS frequency (GPS operates at 1575.42 MHz and 1227.60 MHz).
I guess if there is no straight answer, would it do any harm to connect two antenna ports with a Y cable? any back feeding issues foreseen?

Not sure what aspect you want to share. If you mean connect both at the same time, I suspect that not only will it not work, but it could damage, the antenna, the GPS module or the 433MHz transmitter.
That antenna is an active antenna that is powered by the GPS module.

If you use it as a passive antenna on the transmit device only, it would be a very poor antenna for 433MHz but might increase power of the harmonics that these inexpensive transmitters create. You could easily end up with a transmitting device operating outside its legal limits.
Graham