If their real wealth is not confiscated or expropriated during the process of crytpo-currency adoption, they shouldn't care. Say, you have a house, and its price can be denominated both in dollars and bitcoins (or any other currency for that matter). Does this playing with figures change its real value?
For real estate value is more constant (thats why mortgages exist), however I indeed think the ultra-rich are sitting on heaps of money....well not literally but think of investments, shares, etc. I also think that the market cap that bitcoin represents is partly (mostly?) taken from the market cap of fiat. So yes, in a way, their wealth is expropriated from them because of devaluation.