Well, I am not sure exactly what you mean by "coupled with". In the installation for Visual Studio 2005 Beta 2 you can choose to install SQL Server as well. The version installed then is SQL Server 2005 Express Edition April CTP. You can however use any edition of SQL Server 2005 April CTP with VS2005B2.
I have been using SQL Server 2005 Developer Edition June CTP with VS2005B2 as well. However I do not think you can use the July CTP of Visual Studio 2005 with any existing SQL Server 2005 ctp or beta. Hopefully the August CTP will be out soon (or will it be a B3 or September CTP??) and then we will be able to use a later version of VS2005 than Beta2.
According to the readme that comes with the SQL Server 2005 June CTP, you can use Visual Studio 2005 Beta 2, but you must install SQL first, then VS. I have a successful working environment set up on a MS VirtualPC instance on my laptop of these two, and they are working fine.
My understanding is that the April SQL Server 2005 CTP (beta) was the last co-joined delivery until mid-September or possbily RTM which is slated for approximately two weeks prior to November 7th. If they are going to be used together and are not co-joined then they have to be on separate servers. I am guessing that it is something "simple" that causes this - like they were developed with different versions of the also-beta 2.0 framework. The June CTP requires framework to be uninstalled and then installs a newer version (or at least another version). At any rate, there are enough bugs that it would not be recommended to put them both on the same machine without understanding the implications.