Yes. WFCM Section 3.2.6.1 requires ridge straps, but provides an exception for collar ties: “Ridge straps are not required when collar ties (collar beams) of nominal 1×6 or 2×4 lumber are located in the upper third of the attic space and attached to rafters in accordance with Table A-3.6.”

See the following article for more information:
http://www.jlconline.com/roofing/conventional-roof-framing-a-codes-eye-view_o.aspx