String inside DLL

[abcd]

I prevent to use sharemem unit in my DLL file so I don't use string variable as the parameter.

function Test(const Filename:widestring;var output:widestring):boolean;stdcall;
begin
if Test2(Filename,output) then
bla
end;

functon Test2(const Filename:string;var output:string):boolean;
begin
;
end;

exports Test;

My question, is it safe to use any string variable inside DLL function , even the string variable is not located in function that being exported.