The O/A phonetic distinction in Russian and related languages is tricky, with some dialects making a distinction and some not (https://en.wikipedia.org/wiki/Vow

The O/A phonetic distinction in Russian and related languages is tricky, with some dialects making a distinction and some not (https://en.wikipedia.org/wiki/Vowel_reduction_in_Russian https://en.wikipedia.org/wiki/Vowel_reduction_in_Russian and https://en.wikipedia.org/wiki/Akanye https://en.wikipedia.org/wiki/Akanye) If someone would pronounce Alek and Olek the same, the chosen transcription of the shortened nickname is pretty much arbitrary.