Hi Peter,
Were they, or are they, infected with fire blight, bacterial blast, rust or leaf spot/leaf blight? This is important to ascertain.
If they had any of the above, I wouldn't use them as mulch in a new apple/pear orchard.
If they are healthy by all accounts, then I think you are likely okay to go for it. But, be sure about the infection you might be spreading into your new orchard ground. A little research online will help you to identify a variety of diseases in hawthorns. May be better to just be safe than sorry and chip the material and haul it off site.
You could also consider
not using them as part of your fungal building strategy, as mulch, and high heat compost them in piles first and then use the material. Different purpose, as the new orchard is concerned, but may be better than hauling it off or burning it.
Many Hawthorn diseases can easily jump to apple, crab apples, pears and quince. Around our orchards adjacent ground, we cut hawthorn and burn it each year as it is the number one fireblight host in our area.
Good luck
Gopher Hill ApplesZone 8 in California