I am not so sure. There are statements oposing guest addtions and there are statements oposing these statements and I am not qualified to determine what is true. (Linked on https://www.whonix.org/wiki/VirtualBox_Guest_Additions) (Please open another topic if you like to discuss security of guest additions in details.)
Patrick, why not use the guest additions shared folders once for that purpose?You could do that under the acquirement, that the bug in Debian Jessie's guest additions for mounting shared folders has been fixed in meanwhile. I don't know the current status.