If the hubs are the same or very similar, then sure, the spokes will interchange.
But otherwise, you'd have to be lucky to find a match of length, diameter and angle...
I know nothing about the XL hubs, but I assume the 250 and 500 are the same?
With using the RM spokes on XL hubs, you'd want the RM hubs to have the same diameter flanges as the XL's AND for the flanges to be the same distance apart on the XL & RM.
And you mght still run into dramas with spoke diameter and/or the thickness of the flange on the hub.
Its possible, but I would be surprised!