An IBM blade server is just a form factor of the physical hardware, it doesn't encompass the software or operating system.
You've got three typical types of server form factors:
Tower
Rack
Blade
Each is useful in different ways, but generally Blade servers are used when you need a lot of servers in a small amount of space such as datacenters.
Irrespective of which you choose, your first step is to install an operating system (such as Windows Server 2003, Windows Server 2008, Linux or VMWare vSphere) along with the relevant hardware drivers and manufacturer management tools. After that you'd install Cognos.
So, with that in mind, your question isn't correct, they are not a direct comparison.