Yes.
The second QPI channel with shut itself down, and work (DP parts will work in an SP machine of this particular architecture; the reverse however, is NOT possible <SP processor in a DP machine>).
That said however, the cost of a 56xx part is more expensive, making the use of a 56xx CPU in an SP board not cost effective.
Another note, if you use an i7-9xx, the OEM memory will not operate in ECC mode (i7's do not support ECC; OEM memory is Unbuffered ECC, aka UDIMM), and Registered ECC DIMM's won't work at all with an i7 (RDIMM).