Yes, in CA we can compel a chemical test. Even the USSC says we can compel a chemical test. However, it is the POLICY of a number of agencies NOT to compel blood on anything short of a felony. In your state, there may be a law prohibiting the forced taking of blood - but it would be a state law; it might also be a local policy or practice rather than law.
The arrest requires probable cause to believe that the person is under the influence of a controlled substance. As such, there is probable cause to believe that the evidence is in his body. The exigency is that the body is metabolizing (i.e. destroying) that evidence each and every minute. Ergo, you have probable cause AND an exigency to justify the exception to the warrant requirement.
And, no, "looking high" is NOT sufficient to establish probable cause. It should include the articulated, objective symptoms of being under the influence. And one does no have to be a DRE to make such an arrest, but it helps. I believe am the only DRE trained officer in my county, aside from one of the local CHP officers. But many officers have the lesser DAR class, or simpler still "11550 training." I used to be tapped by everyone to go out and bless their dope influence arrests ... now, thank God, they have enough people who are minimally trained to do the job.