The question "How was Samson not in violation of his Nazirite Vow?" (while judging Israel for 20 years) disregards Samson's confession to Delilah in Judges 16:17 divulging the Naziriteship of his hair.
[Shoftim | Judges 16:17] "And he told her all his heart, and said to her, "A razor has not come upon my head, for ** I am a Nazirite of Elohim from my-mother's-womb **. If I will be shaven, then my strength will leave me, and I shall become weak and be like any man." ( וַיַּגֶּד־לָ֣הּ אֶת־כָּל־לִבּ֗וֹ וַיֹּ֚אמֶר לָהּ֙ מוֹרָה֙ לֹֽא־עָלָ֣ה עַל־רֹאשִׁ֔י כִּֽי־נְזִ֧יר אֱלֹהִ֛ים אֲנִ֖י מִבֶּ֣טֶן אִמִּ֑י אִם־גֻּלַּ֙חְתִּי֙ וְסָ֣ר מִמֶּ֣נִּי כֹחִ֔י וְחָלִ֥יתִי וְהָיִ֖יתִי כְּכָל־הָאָדָֽם )
Did שִׁמְשׁ֑וֹן Shimshon tell דְּלִילָ֜ה Delilah that his strength was from a Nazirite vow [he made] to curl his hair? - No. | In Shoftim (Judges) Chapter 16 verse 17, Shimshon confesses to Delilah that the strength of his hair (Naziriteship) was from his mother's womb. - It was Manoah's Wife who made the Nazirite vow in Shoftim 13:3-7 never to drink wine or cut Shimshon's hair in dedication of her son to Elohim.
- In Shoftim (Judges) 13:3-7, we learn the Angel of YHVH (מַלְאַ֨ךְ יְהֹוַ֜ה) and the Wife (הָאִשָּׁ֗ה) of Manoah (מָנ֑וֹחַ) make the Nazirite vow for Manoah's son - Shimshon שִׁמְשׁוֹן "Samson" to hopefully become a Nezir (נְזִיר) of God to save Israel from the hand of the "Philistines" פְּלִשְׁתִּֽים Phelishtim .
[Shoftim | Judges 13:5] "Because you shall conceive, and bear a son; and a razor shall not come upon his head, for a [Nazirite] of Elohim shall the lad be from the womb; and he will begin to save Yisrael from the hand of the Phelishtim" ( כִּי֩ הִנָּ֨ךְ הָרָ֜ה וְיֹלַ֣דְתְּ בֵּ֗ן וּמוֹרָה֙ לֹא־יַעֲלֶ֣ה עַל־רֹאשׁ֔וֹ כִּֽי־נְזִ֧יר אֱלֹהִ֛ים יִהְיֶ֥ה הַנַּ֖עַר מִן־הַבָּ֑טֶן וְה֗וּא יָחֵ֛ל לְהוֹשִׁ֥יעַ אֶת־יִשְׂרָאֵ֖ל מִיַּ֥ד פְּלִשְׁתִּֽים )
Regarding the Nazirite vow in Bamidbar (Numbers) 6:2-9, a mother cannot make a Nazirite vow for her son. The vow must be made by a Yisraelite man or woman who sets themself apart to become holy for God.
Shimshon שִׁמְשׁוֹן never makes the Nazirite (נָּזִ֗יר) vow. - Shimshon prays only twice during his life to YHVH requesting a post-battle beverage in Judges 14:18 & later in Judges 16:28 for vengeance against the Phelishtim פְּלִשְׁתִּֽים "Philistines" after being humbled by the removal of his Einay עֵינַ֖י "Eyes".
Samson's Prayer in [Shoftim (Judges) 16:28]: "And Shimshon called to YHVH and said, "Lord YHVH, remember me and strengthen me now, only this once, God, that I may be avenged the vengeance for one of my two eyes from-[the]-Phelishtim." ( וַיִּקְרָ֥א שִׁמְשׁ֛וֹן אֶל־יְהֹוָ֖ה וַיֹּאמַ֑ר אֲדֹנָ֣י יֱהֹוִֹ֡ה זָכְרֵ֣נִי נָא֩ וְחַזְּקֵ֨נִי נָ֜א אַ֣ךְ הַפַּ֚עַם הַזֶּה֙ הָאֱלֹהִ֔ים וְאִנָּקְמָ֧ה נְקַם־אַחַ֛ת מִשְּׁתֵ֥י עֵינַ֖י מִפְּלִשְׁתִּֽים)
Vengeance for one of your eyes?? -- What about vengeance for your Nazirite hair that was just cut off to dishonor your mother's vow to YHVH?
We are told in Judges 16:22 that the Naziriteship of his mother's womb could not lose its strength!
[Shoftim | Judges 16:22]
"And the hair of his head began to grow after he was shaven." ( וַיָּ֧חֶל שְׂעַר־רֹאשׁ֛וֹ לְצַמֵּ֖חַ כַּאֲשֶׁ֥ר גֻּלָּֽח )
The strength of his Nazirite mother lived in Samson's hair. The vow of Manoah's Wife made Shimshon's hair curl. | The strength of Shimshon's arms came not from any Naziriteship but when the Ruach YHVH ר֣וּחַ יְהֹוָ֗ה "Spirit of [the Lord]" rested on him, as stated in Judges 14:6.