Hi Atle,

Yes we need a common l2 platforms for the vlans configure on the UCS since the two FI create two different fabric (A&B) and any traffic from A for blade on B and vice versa will need to be switched by the upstream switches. if you do not have a common point above the 3560 and the 3750 then you need to have a link between the two switches. Do make sure to allow the vlans (configure on ucs and others if required) on those ports as well as make sure the spanning-tree is not blocking them.

i am not very sure about your second questions, however on what ever i understand:

1) if you have multiple links going to the same switch its prefered to put them in a PO

2) since these switches are different and not in a VSS, you will need seprate Po for each switch.

Hope this helps!

./Abhinav