Wight and Wiht is white?
Wight is etymologically unrelated to white. The former is pronounced /waɪt/; the latter is pronounced /waɪt/ (the same as wight) or, in certain conservative accents, /hwaɪt/ or /ʍaɪt/ (the transcriptions /hw/ and /ʍ/ don't contrast; the difference is just that the transcription /hw/ implies analyzing the "wh" sound as two phonemes, and the transcription /ʍ/ implies analyzing the "wh" sound as one phoneme).
Dutch wit /ʋɪt/ is just a cognate of white, with a hard-to-explain difference in vowel length (which in older versions of the language apparently went along with a long /tː/ sound after the vowel). Its pronunciation has nothing to do with wight either. The Dutch cognate of wight is wicht /ʋɪxt/.
Both wight and white have the "/aɪ/" diphthong sound (the vowel found in the word price) because of the "Great Vowel Shift". Before the Great Vowel Shift, these words were pronounced with /iː/. In the word white, this goes back to Old English forms with a long vowel. In the word wight, the long vowel developed during the Middle English time period from an earlier short vowel + consonant sequence that can be transcribed /ih/, or possibly /ix/. The /h/ or /x/ sound here was a voiceless fricative consonant. As in German, the sound /x/ was probably assimilated to the palatal fricative [ç] when it followed the "front vowel" /i/. Early on, the spelling "h" was often used for /x/, but in modern English, the digraph "gh" has completely replaced earlier spellings with "h" in words that once had /x/. The spelling wiht is even more obsolete than the word; as Laurel said, wiht really ought to be thought of as a Middle English spelling, not a modern English one. The Middle English word wiht would have been pronounced something like [wɪçt], [wiçt], [wiːçt], or [wiːt].
Vowel sounds could develop differently in different dialects or in different contexts. For example, /(h)wɪt/, with a "short i" sound, is used as the pronunciation of the combining element Whit-, which is derived from white. (Some examples: Whitsunday, Whitman.) Wight is the (hard to recognize) source of the final element of the words nought/naught, not, and ought/aught. If the word wight has actually survived as part of the living vocabulary of any currently spoken English dialect (I don't know whether it has), it wouldn't be too surprising if the speakers of that dialect used some pronunciation other than /waɪt/.
The word whit (/(h)wɪt/) has unclear etymology, but might be related to either wight or white according to the Oxford English Dictionary.
When the word wight is used to refer to a creature in the context of fantasy (e.g. Tolkien's The Lord of the Rings), neither the spelling wiht nor the pronunciation /wɪt/ seems sensible to me. The spelling wiht could be justified as an Old-Englishism, but I know of no justification for using the pronunciation /wɪt/ in that context. If you have heard it, I'd guess it was a mispronunciation based on the spelling pattern "ih" = /ɪ/ that is used in some ad hoc representations of English vowel sounds. Many words used in fantasy are first encountered in writing, and therefore commonly mispronounced (although the term "mispronunciation" is only applicable insofar as they can be said to have any standard pronunciation at all).