No, his rights weren't "violated". Simply talking to a suspect while he is "under the influence" does not render the questioning invalid.
Here are parts of two articles about Miranda warnings from the Alameda County DA's office:
SUSPECT INTOXICATED, HANDICAPPED: Even though a suspect said he understood his
rights, he may later claim he didn’t because his mental state was impaired by alcohol or
drugs, physical injuries, a learning disability, or a mental disorder. Suspects for whom English is a second language may also contend they did not understand if the officers spoke in English.
As a practical matter, however, the courts almost always reject “I didn’t understand”
arguments if the suspect’s answers to the officers’ questions were responsive and
coherent. This is because a suspect’s rational responses demonstrate that he understood
the officers’ questions which, in turn, indicates he also understood the Miranda warning.
Although less important than the suspect’s fitting responses, the courts sometimes
take note of his age, experience, education, background, and intelligence; whether he
had been arrested or advised of his Miranda rights before, and whether he had
previously invoked.
Alcohol and drugs
The courts recognize that suspects may understand their rights even though they are under the influence of alcohol, drugs, or both. As the Court of Appeal observed, "[N]either the consumption of alcohol nor ingestion of drugs alone compels the conclusion that a defendant is incapable of intelligently waiving his rights."
In cases where a suspect claims he did not understand his Miranda rights as the result of consuming alcohol, drugs, or both, the courts will usually look to see whether the suspect's answers to the officer's questions were responsive and coherent. If so, the suspect's claim will usually be rejected. For example, waivers by intoxicated suspects have been deemed "intelligent" based on the following circumstances:
The suspect, whose blood-alcohol content was between .14 and .22 percent, "made meaningful responses to questions asked" and "nothing indicated that defendant was anything but rational."
The suspect "had been drinking and had a history of emotional instability" but was "able to respond to the questions asked of her coherently."
Although the suspect appeared to be under the influence of "some drug," his answers were "logically consistent."
The suspect was under the influence of PCP but his "answers were rational and directed to the questions."
The suspect had ingested a small quantity of alcohol and drugs but "acted sober and appeared to understand the proceedings."
Although the suspect's blood-alcohol content was approximately .21 percent, the arresting officer testified he "would not have arrested him for being 'plain drunk.' He also testified that while [the suspect's] condition was such that [the suspect] could not safely operate a motor vehicle, he otherwise knew what he was doing."
The suspect was shaking as the result of the onset of narcotic withdrawal but he "spoke coherently and the officer had no trouble understanding him."
Although there was testimony that the suspect was "loaded on alcohol and drugs," he admitted that he understood his Miranda rights.