Yes they do. I am in the process of doing it right now. Basically, go to the Adobe web site, find the customer service number and call them up. When you get to a representative, tell them that you want to transfer your existing PC license for Photoshop to Mac. They will point you at a form called a Letter of Destruction and ask you to fill it out and either fax or email it back to them. This form certifies that you have destroyed your PC copy of Photoshop. When they receive you completed Letter of Destruction form, they go ahead and ship you out a new Mac version. It takes about a week to get through the first step here (get the form, fill it out, send it back, and wait for them to review it and authorize the shipment of a Mac version to you). It takes 7-10 business days after that to actually receive your new Mac version.
I am presently (and impatiently!) in that 7-10 day shipping interval.
So, go ahead and give them a call. They are very helpful about it all.