Not really. They have to keep a certain amount in bonds to match their insurance liabilities long-term, but outside of that, they have enormous flexibility in what they can invest in.
They also run models on what would happen to them if there were two major catastrophes in a given year (I believe they use a 9.0 earthquake in Los Angeles and a F5 hurricane hitting Florida combined with a 50% drop in the U.S. market).
So as long as their models stay intact with the investment ideas they use, and possible outcomes with those ideas, they can invest in almost anything.
Cheers!