You can install and run the SSIS Designer in 32 and/or 64bit on the same 64bit OS. I guess it will depend in your case on what type of OLEDB you have available. Oracle has both 32bit and 64bit available. You need to choose as required by your environment/application needs. See bottom for link with complete MS article; I've pasted what I thought was relevant:
"When you run a package in 64-bit mode, you might not be able to connect to as many data sources as you can when you run a package in 32-bit mode. Some .NET Framework Data Providers and native OLE DB providers might not be available in 64-bit versions. For example, the Microsoft OLE DB Provider for Jet, which connects to Access databases and Excel spreadsheets, is not available in a 64-bit version. Also, the SQL Server Compact Provider, which connects to SQL Server Compact data sources, is not available in a 64-bit version."
"Running Integration Services Packages on 64-bit Computers
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Sometimes you might want to run packages in 32-bit mode on a 64-bit computer. You might want to run packages in 32-bit mode for the following reasons:
•To run SQL Server 2000 DTS packages.
•To use a managed .NET Framework Data Provider or native OLE DB provider that is not available in a 64-bit version.
•To use a Script task or Script component that references other assemblies or COM components for which a 64-bit version is not available or not installed.
Selecting 32-bit or 64-bit Package Execution in SSIS Designer
In the Project Properties of an Integration Services package, you can select 32-bit or 64-bit execution by setting the value of the Run64BitRuntime property on the Debugging page. By default, the value of this property is True. When the 64-bit version of the Integration Services runtime is not installed, this setting is ignored."
From:
http://msdn.microsoft.com/en-us/library/ms141766.aspx
