Yes, Ukrainian displaced individuals are allowed to study in the Netherlands. For clarification, this includes all types of education beyond secondary school: vocational education (mbo), higher professional education (hbo), and university education (wo).
For all studies in Dutch, an admission requirement is that your guest has passed the Staatsexamen NT2-II (State Examination Dutch as a Second Language, level II). For all studies in English, there is a requirement to pass an IELTS or TOEFL exam.
Furthermore, your guest’s previous education will be taken into consideration. This is done by having the diploma evaluated by the International Credential Evaluation (IDW). You can initiate a free application here. If the diploma is not sufficient, for many programs, especially in vocational education (mbo), there is also an admission test for those aged 21 or older.