Upgrading SQL Server with Integration Services
As per BOL


  When you upgrade to SQL Server 2014 Integration Services (SSIS) on a
  machine that has one of these earlier versions of Integration Services
  installed, SQL Server 2014 Integration Services (SSIS) is installed
  side-by-side with the earlier version.


It also says that:


You can upgrade by using one of the following methods: Run SQL Server
2014 Setup and select the option to Upgrade from SQL Server 2005, SQL
Server 2008 or SQL Server 2008 R2, or SQL Server 2012.
Run setup.exe at the command prompt and specify the /ACTION=upgrade
option. For more information, see the section, "Installation Scripts
for Integration Services," in Install SQL Server 2014 from the
Command Prompt.


Source

Now, as per my personal experience with In-Place SQL Server upgrade from SQL Server 2008 R2 to SQL Server 2012 I didn't face compatibility issues. Packages ran fine, except for few where I had to open packages and compile script task again.