Can I use two DC-DC Converter modules to generate a +5V and -5V Rail?
The short answer is not the way you have described: these are non-isolated converters.

As you can see in the picture (from the web site), there is a single ground pin (for both input and output).



To achieve what you want to do you can either use isolated converters or you can use two of them in this manner: use one to get 5V; power the second one from this 5V to get a negative output provided your total load is within the current allowed from the first regulator.



As these are rated for 36V you should be fine - the second regulator will see an effective 10V in to out.

I made a picture of two regulators showing how I would hook them up for +5V and -5V:



Hopefully that is clear.