If I'm correct, you're showing this as a counter example to prove that the two have incompatible APIs and are thus LoDash can't be used ad a drop in replacement. However, Lodash does alias it's 'forEach' function with 'each', so this wouldn't be an issue?
underscore.each has an optional 3rd parameter (context). lodash.each does not. If you depend on that 3rd parameter, you will be in a world of pain if you drop-in lodash. In fact you'd be better off if there was no alias because you would catch the problem sooner and have to think about the API differences when fixing it.