Hi there,
I´m not sure what the Edgemark voip router does, please attach a link or something so I can have a look :-)
In short
Your 3560 will probably have the vlan and ip configuration. Have you specified "ip helper address" that directs dhcp requests to the edgemark?
The requests are not bound to any vlan and can traverse many networks to get to the destination and back. Depending on you size and design of the nework, the requests can take odd paths to reach the dhcp. Anyway, if you specify the helper address the router will send the request the best way to reach the dhcp. At least, they should not "leak" to any other network that is not specified in the helper address command
If the edgemark is placed locally on the same vlan it will catch the requests anyway so you do not have to do this if the phones are just local as well.
Not sure if that answered your question, but that´s how it works.