Poole/Bournemouth is surprisingly multicultural in some ways, despite a relatively low number of visible ethnics.
There are very long established Spanish and Italian communities dating from post WW2 migrations of people coming to work in care homes and hotels. And a later wave of east Europeans coming into take the same jobs. It is very very common to hear families speaking Slavic languages on the prom, and equally common to come across families where one partner is British and the other from Europe.
There is other diversity. One more obvious one is the large Jewish community, both Orthodox and non Orthodox, boosted in the summer by Jewish holiday makers, most noticeably by large Orthodox family groups. There is a very long established Armenian community. I was once in a cafe and every other table was taken by South Africans. Apparently at the point when it became obvious that they were never going to return to South Africa, families often made the decision to migrate from SW London to Bournemouth/Poole in search of a more outdoor lifestyle. Whilst in summer it becomes clear that British beach holidays and day trips have been adopted by more recent British groups, so it is very common to see extended Asian families or groups of West Africans on the beach enjoying picnics and with kids racing into the sea.
The Universities obviously add diversity, with students then staying on to work, and I have rented to Chinese, South Africans and a British Muslim students. The latter, who came from a deprived part of the East End, loves it and intends to stay post-graduation. A bit like my dad who was evacuated to Bournemouth during WW2 from New Cross and who retained a wonder for the beach and space. For him it was always paradise.
That said, Bournemouth/Poole is surrounded by low populated, rural areas and is more Dorset than many expect. If it offers the lifestyle you want, I would expect you will find most people welcoming, and some people are jerks. My own impression, as a white Londoner, who needed a lot of help and support during a decade when my mother was ill, was that most people were very kind, far beyond what I would have expected in London, and that these people were white, or Bournemouth Asian (the night my mother died I phoned our favourite curry house at 11.00pm asking if we could pick up a take away on our way to the hastily booked hotel, but instead they stayed open and insisted we ate there), Bournemouth Jewish, from central Asia, Chinese, mixed race, or whatever.