As you read this response, please bear in mind that this is a public forum on a website, and that this answer does not create an attorney-client relationship, nor is it legal advice; it is simply an answer to a question asked in a public forum. Because it is a public forum, nothing said on this site is confidential or covered by privilege. As with anything in the law, there are exceptions to every rule, and you need to consult an attorney in your area for the best answer. Also, because of regional differences in practice, even within a state, what works in one area may not work in another.
Each State is different, but there is no requirement that I am aware of in any state that requires that charges be filed on the date of the offense, except maybe a traffic ticket. It sounds to me like the officer chose to wait on the results of the blood test before deciding whether he would file the DWI charges against you. Once they came in (it can take months at a state lab), he filed the charge and a warrant was issued for your arrest.
Typically, the only limit on how long he may wait to do so is the Statute of Limitations. In Texas, the Statute of Limitation son misdemeanors is two (2) years. In other words, if he had arrested you on September 1, 2008, the State would simply have to file their charges before September 1, 2010, and there is no problem there.
The Statute of Limitations will vary from state to state, but I would be shocked if six to eight months was too long to file the charges. You will want to consult with an Arizona lawyer about this, but I would strongly recommend that you get yourself a lawyer who is experienced with DWI defense, especially for a breath- or blood-test case. It's a different animal, and you want someone who knows the area well.
Like the previous answer suggested, the state can ordinarily file a criminal charge any time within the statute of limitations.
In your case, since they could not get the summons to you due to a problem with delivery, the only thing they can really do is issue a warrant for you so that you will end up in court to answer the criminal charges against you.