I would like to omit the nuts, does this require an additional substitution?

Nuts are an add in/optional thing in baking. No Problem with omitting them!

I'm allergic to nuts, so routinely leave them out without any problems.

A recipe like this, it should be fine to leave out the nuts. It will change the flavour and texture not to add nuts, but it looks like it will still be delicious.

Quite often I'll substitute raisins or other dried fruit if I don't want crunch. You don't need to toast them, but sometimes raisins soaked overnight in rum add an extra special touch.