In order to sentence a defendant to a "dangerous offender" sentence, there must be a finding of a severe personality disorder.
161.725 Standards for sentencing of dangerous offenders.(1) Subject to the provisions of ORS 161.737, the maximum term of an indeterminate sentence of imprisonment for a dangerous offender is 30 years, if because of the dangerousness of the defendant an extended period of confined correctional treatment or custody is required for the protection of the public and one or more of the following grounds exist: (a) The defendant is being sentenced for a Class A felony and the defendant is suffering from a severe personality disorder indicating a propensity toward crimes that seriously endanger the life or safety of another. (b) The defendant is being sentenced for a felony that seriously endangered the life or safety of another, the defendant has been previously convicted of a felony not related to the instant crime as a single criminal episode and the defendant is suffering from a severe personality disorder indicating a propensity toward crimes that seriously endanger the life or safety of another. (c) The defendant is being sentenced for a felony that seriously endangered the life or safety of another, the defendant has previously engaged in unlawful conduct not related to the instant crime as a single criminal episode that seriously endangered the life or safety of another and the defendant is suffering from a severe personality disorder indicating a propensity toward crimes that seriously endanger the life or safety of another.
At the state's request, "the court may appoint one or more qualified psychiatrists or psychologists to examine the defendant in the local correctional facility." ORS 161.735(1).
That said, I can't imagine any obligation that the defendant has to comply with the evaluation. This isn't a situation where the defendant has given notice of an affirmative defense, such as extreme emotion disturbance or guilty except insane (and even in such cases the evaluations are quite limited in scope). The sole purpose of the evaluation is the state's attempt to learn something from the defendant that they can use to lengthen his sentence. In other words, the defendant has a right to remain silent. Pretty basic.
But the state may still proceed anyway, by having their own psychologist or psychiatrist attempt to reach a diagnosis based on jail or prison records, police reports, juvenile records, etc.
Two things: first, you should of course hire your own psychologist, whether or not you have him or her evaluate the defendant, just to have them explain the weaknesses in any diagnosis that does not involve actually interviewing the defendant. And there are lots of weaknesses.
Second, be prepared for the following scenario, where the state's expert does not actually diagnose your client with a severe personality disorder, but the state seeks to offer their testimony to explain to the finder-of-fact what a personality disorder is. The idea being that the jury - or judge, in a bench trial - will make the necessary leap themselves, and find a severe personality disorder that no expert has diagnosed.
Such an effort by the state is impermissible, as demonstrated by the following two holdings:
Implicit in respondent's argument was the idea that the jury, having heard evidence of abuse and expert testimony about BWS, could reasonably deduce that complainant behaved as a battered woman. The proposition that the jury could diagnose BWS was rejected as a matter requiring expert testimony. Since complainant was not diagnosed as a battered woman, evidence about the behavior of battered women was not relevant.
State v. Ogden, 168 Or App 249 (2000)
And. . . .
In each of those cases, expert testimony regarding the effects of a specific psychiatric disorder was offered to explain the behavior of a person who had not been diagnosed as having the disorder. We held that testimony regarding the effects of the disorder was irrelevant because, without an expert diagnosis, the jury was not qualified to determine whether the person actually suffered from the disorder. Tush, 179 Ore. App. at 441-42; Ogden, 168 Ore. App. at 256-57. In this case, although Larsen's affidavit shows that some people undergoing methamphetamine withdrawal are unable to form specific intent, nothing in the affidavit shows that he would have been able to testify that petitioner was one of those people. Thus, if expert diagnosis is required, Larsen's proposed testimony would have been inadmissible and, therefore, could not have affected the verdict."
Short v. Hill, 195 Or App 723, 729-730 (2004)