with $sudo apt-get install freetds-bin libsybdb5 there are the correct freetds drives on Raspi for MS-SQL installed in
/usr/lib/arm-linux-gnueabihf/libsybdb.so.5 (=link)
/usr/lib/arm-linux-gnueabihf/libsybdb.so.5.0.0
with ZEOS you can access now
// SQLCon is a TZConnection from ZEOS
DebugLn('Using Linux Connection');
SQLCon.Protocol := 'FreeTDS_MsSQL>=2005';
{$ifdef RasPi}
SQLCon.LibraryLocation:= '/usr/lib/arm-linux-gnueabihf/libsybdb.so.5';
{$else}
SQLCon.LibraryLocation:= '/usr/lib/x86_64-linux-gnu/libsybdb.so.5.0.0';
{$endif}
SQLCon.HostName:= 'MSSQLServer';
SQLCon.User:= 'jondoe';
SQLCon.Password := 'secret';
SQLCon.Database:= 'mytestdb';
SQLCon.Properties.Add('appname=MyWorkingApp');
This code is working for me on Debian (PC) and Rasbian (RasPi3). Also on windows PC with the correct driver-dll.
Actual i have not found to change the drivers-nane and position in SQL-DB.