Too nicknamey as a name in its own right for me personally, I’ve never really liked it. I love [name_f]Hettie[/name_f] but I’d still want a long form. However I wouldn’t be surprised to hear someone was called just [name_f]Hattie[/name_f], as nicknames-as-names is a popular category.
[name_m]Just[/name_m] realised it’s a revived old thread 
I personally don’t like Hattie as a stand alone name, but I love Hattie as a nickname for Harriet or Henrietta. I just in general don’t like traditional nicknames as legal given names.
I love [name_f]Hattie[/name_f] as stand alone name.
Something like [name_f]Hattie[/name_f] juniper or hattie clementine 
[name_m]Just[/name_m] [name_f]Hattie[/name_f]