Depends upon which part of the river you are fishing. The lower portion near 101 is entirely private, no public access. The only time to find sea run cutts down there is in mid-September, bu then the river is closed until Nov. 1st. If you are targeting the upper section, standard wets will catch the planted bows.
I have never fishied the Hamma Hamma itself, but I have looked into it and fished nearby waters. I think that simple attractor dries would be great, with a few BH pheasant tails as backups. My favorite creek fly is a size 12 Irristible Wulff- it is amazingly visible, floats like a cork, and trout take it with gusto. Good Luck (hope this isn't too late)-