These converters from Pololu look great (https://www.pololu.com/product/2831), but I need both a positive and negative rail. Can I use two of these to make a +5V and -5V rail? For example. if I tie the + terminal on one to the - terminal on the other and tie that node to ground and then use the respective output terminals as +/-5V rails, would that work?
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.
Look at the schematic of this converter. If you do what you suggest, it means you tie the 5V output of the second converter to ground, thus shorting it.
So, no, since they are not isolated, you can't wire these converters as you suggest. You need isolated converters to do this. Isolated converters have a transformer that allows this.
Or another option would be to use a non-isolated inverter DC-DC converter. They are easy to find and would be cheaper and smaller than isolated ones, I think (There are none on polulu, it seems, though. Try mouser/digikey).
No you can't because that would short circuit the - 5 V converter as the input ground and the output ground are the same node.
It actually has only one connection pin !
What you need is a regulator with an isolated output for the -5 V. Then the output is floating and you can use it to make - 5V. Some examples of these are here.