Yes, it is tonal. I suppose that the idiom is not far removed from Rautavaara and Part but he has a unique and recognisable style.
I'm not commenting on you personally, because this sort of thing is often said about Vasks, and others of this type (Kancheli being a prominent name worth mentioning); it's the sort of thing I have to stop myself from saying too. But it seems to me to be a little lazy and potentially misleading (and after all, Rautavaara and Part are very dissimilar composers themselves).
Part is a very special case, even amongst composers closer to him such as the ubiquitously cited Gorecki or Tavener. Part is the only one of these composers, AFAIK, to use a strict system in all his stylistically mature compositions (especially those written when he first developed the system, as we discussed yesterday on the Part thread). Though intensely attractive music appealing to a wide audience, Part's music is in essence as process-driven as some of Ligeti's
Etudes, in its own way. For this reason he stands apart from all the other composers often lumped together with him. Gorecki and Tavener
are the closest, though it's even more of a cliche to say so, because they too often use prominent process-driven forms (witness the infamous canon of Gorecki 3 or the mirror-harmonies of
The Protecting Veil, to cite these two composers' respective strike-it-big works), but there's nothing on the level of Part's all-pervasive system even in their music.
So, to be more detailed:
What Vasks shares with Part - predominantly slow tempi and subdued dynamics; relatively simple tonal harmony; repeating figures and a generally 'spiritual' tone
Where he differs - Part doesn't develop his material, Vasks does; Part almost never uses fast tempi, Vasks does; Part avoids climax, Vasks doesn't; Part uses process in every note, Vask doesn't.
IOW, Vasks is more of a 'romantic', aesthetically speaking, than Part, who is very much a minimalist in these respects at least.
