Contributing other person's work

[조성빈]

I would like to contribute a patch to emacs (which adds Emacs xwidget webkit 
support for macOS Cocoa), but most of it was developed by another person (I 
just updated the patch periodically as some Emacs internals changed); see 
https://github.com/veshboo/emacs

He indicated his intention to contribute to mainline (see 
https://lists.gnu.org/archive/html/emacs-devel/2017-11/msg00662.html and 
associated messages); and a comment in one of his issues (see 
https://github.com/veshboo/emacs/issues/5#issuecomment-421777014) indicates 
that if veshboo(Jaesup Kwak) signed his FSF copyright assignment,  others can 
do the integration for him.

Is this true? (If it’s true) Is there a way to check if one has signed the FSF 
copyright assignment?