You have to sign the FSF's CLA (and clear your contributions with your employer) to contribute to Emacs itself. To ship a separate package to ELPA you need not do this.

A point of clarification: GNU ELPA (https://elpa.gnu.org/) is part of Emacs, and you have to sign the copyright assignment to submit packages an to contribute to packages. NonGNU ELPA (https://elpa.nongnu.org/) doesn't have this restriction.