Answering based on system defaults (because of lack of the information in the question):
[~]# ls -ld /Library/WebServer/Documents
drwxr-xr-x 5 root wheel 170 Feb 21 2016 /Library/WebServer/Documents/
[~]# ls -l /Library/WebServer/Documents
total 72
-rw-r--r-- 1 root wheel 3726 Feb 21 2016 PoweredByMacOSX.gif
-rw-r--r-- 1 root wheel 31958 Feb 21 2016 PoweredByMacOSXLarge.gif
-rw-r--r-- 1 root wheel 45 Jun 12 2007 index.html.en
Members of group wheel
do not have write permissions to neither tothe /Library/WebServer/Documents
directory nor the files inside.
Hence adding any account to the group wheel
will not allow this account to write files in/to the above directory.