Hi Mike,
The helix angle does not really come into play in the mathematical formulas for feeds and speeds (which mainly link the feedrate, number of flutes, and RPM). Not to say that the helix angle does not matter, it very much does for the quality of the cut, chip evacuation, etc…, but just not for the feeds and speeds that Fusion360 manages (or at least not that I am aware of!)
There was an interesting discussion about the helix angle implications here recently:
If you want to keep track of the helix angles for each endmill in your tool database, indeed the easiest is probably to just add that info in the “description” field for each tool. The tool Pros here will probably chime in, I’m just an enthusiastic amateur!