Scenario 1 is giving a specific example of enabling the same Spanning Tree protocol on both the Cisco and the M8024-k switches.  Scenario 3 is adding to that option giving an example of how to allow multiple VLANs across that same LAG (Link Aggregation).  It is not an either or situation.   Theoretically you will not need spanning tree enabled on the 2 switches if this is the only switch to switch connection.  The LAG is seen by spanning tree as a single cable connection.  Thus no blocking would take place or be needed to keep a loop free environment. That said,  I would still recommend leaving spanning tree enabled.  It will not hurt to have is running.  It is best practice to have it enabled on your switches.  Their are different commands available to manipulate spanning tree on different ports.  Such as portfast.  It allows a port with an edge device to immediately go into a forwarding state.
We have two m1000e blade chassis, each with 2 m8024-k switches.  We are using this document (see link below) to connect them to four cisco 5k's.  [URL] We chose to use Scenario 3 (page 15) in the document.  The first Scenario (Scenario 1, page 5), shows enabling spanning tree before setting up the LACP on the m8024-k, but no other scenarios in the document do that.  So if we are using Scenario 3 we would not do the enabling of spanning tree, is this correct?
connecting m8024-k switches to cisco 5k