Isn't a married couple a single financial entity? Or are you thinking the cup car might have been able to be safe in Mike's racing services business?
Not necessarily. MHR should have been setup as a separate business legal entity (LLC, Corp, etc.). That org has its own books, etc. Then the shareholder(s) can then take a dividend and/or salary out of the business to pay themselves. Mike is a sophisticated businessman - I'd be surprised if he didn't do this.
So, the business itself might be a marital asset - that's what divorce court is for to sort through this stuff. But the day to day cash/income/expenses should all be separate from personal assets. If they aren't kept separate and are instead "commingled," the shareholders lose the protection of having a corporate form as the firewall between their personal and business assets. Shareholders don't just get to stick their hand in the till without receipts, etc.
If the business goes bankrupt and if the shareholder commingled assets, then the creditors can "pierce the corporate veil" and go after the person's personal assets.
Unless Mike's wife raced, the question I'm asking is why is she using the MX5 Cup for restitution if it was an asset of the racing business? Asked another way, how did the ill gotten personal gains make their way to buy an asset for the racing business? Don't expect a definitive answer because Mike I imagine and speculate that Mike has been (and rightly so) been advised not to speak on this topic.
The same argument can be made for the truck and trailer but they can be argued to be "dual use," used for other purposes other than the racing business. Once again, there's no way to know the exact legal position they are taking.
(I have more than a passing interest in this topic. The vast majority of my LinkedIn posts are about the intersection between law & racing. Indeed, I've even attended and spoke at The Racing Attorneys Conference (TRAC) - yes, there is such a thing. Fun fact, the last time I went, I met Tony Stewart's criminal lawyer and Bill Simpson. (he told me a cool story about the Mazda firesuit commercial.))