Answer is 'Yes' for both questions.
You can configure 3511 to use either Skinny or H323 protocol. If configure as Skinny, then it is just another CFB in CM; CM will allocate it as per MRG and MRGL configuration. If configured as H323, then you have to configure 3511 as H323 gateway in callmanager and have a RP to point to the gateway. Typically, the RP will be your conference ID number.
7985 is just another video phone like VTA with an IP Phone; and they do support same type of codecs. Hence you can use 7985 to do video call with VTA as well to do conference with an MCU.