I can't help you with your question as I'm in a way colder zone than you but I just wanted to say that I'm really sorry to hear about your dog's passing. I have 5 pets and they are like my kids so I can't imagine how awful it would be to loose one. I think your memorial garden idea is great. What a nice tribute to your beloved Doberman.
Jason

Wood ashes tend to be alkaline, but I am not sure what is used in cremation. You could prepare your bed and mix everything together then use a soil tester from a big box store to test the PH of your soil, (always a wise idea). You can add whatever might be needed before you plant....it probably won't be a huge problem. I am so very sorry you lost Julian. It is a real loss of a member of your family.

I hope your garden is everything you have in mind for it.
kay

What a lovely idea. The ashes won't change the soil- don't worry about it. If your zone 9 is in California, you can grow all sorts of tall bearded irises. Rita started a thread about good online iris sellers- take a look at that. The flowers come in just about every color but red, and as you browse the catalogs online, perhaps the name of an iris will appeal to you for your doggie.
Renee

Here is a link that might be useful: Stanton Irises