We've discussed this sort of thing before, but I don't agree. It's certainly true that doing running at a BW of 250lbs is much more rough on the body than, say, 150lbs, but there is little-to-no evidence that running shoes improve this situation at all. If anything, they may make it worse by encouraging heel striking. In other words, VFFs should be no worse - and possibly better - than shod running. Of course, after a lifetime of wearing shoes, it'll take considerable time to adapt to VFFs/barefoot and you can't just jump into it at 100% from day one. However, I just don't buy the argument that using VFFs is inherently more unsafe than running shoes.
The problem is this: per 100lbs of body weight, he putting 3-5 extra pounds of force on the major joints of his body. He is likely putting greater amounts of force through the small joints within his feet. Firstly, I'm honestly saying that, at 250lbs, he should rethink running at all - barefoot or not. Individuals that heavy have a severely increased risk of injury.
On top of that, think of how you run barefoot - forefoot strike first, utilizing an eccentric contraction of your gastrocnemius and soleus to slow dorsiflexion and passive tension through the plantar fascia and flexor hallucis longus. In addition, the user puts a massively increased amount of pressure on the metatarsal heads of the foot, a fact overlooked in nearly all barefoot studies. All of these structures, by function, are at increased risk of injury due just to the increased demand. It's sad that research for barefoot running has been so biased as to not produce many objective studies looking at forefoot strike with both shoes and barefoot. In the research I've seen, the pressures for shoes are less (on the met heads) and the overall ground reaction forces are the same... so that means less strain on the plantar fascia, less pressure on the metatarsal heads, etc if you can run correctly. I'm going based off of anatomy that I know will be reported in research soon enough. If I had the resources, I would honestly measure it myself. Look at the anatomy - it may change your mind.
And again, my point is that running period is an inherently risky activity at 250lbs. Add increased pressure on the met heads, increased passive dorsiflexion (which most people don't have and compensate through eversion, leading to flattening of their medial longitudinal arch, leading to stretching of the plantar fascia and frequently plantar fasciitis), and a non-evaluated foot and it's bad news bears. Even if there isn't research about barefoot running vs. shod running, there is research about foot abnormalities and risk of injury in normal activities of daily living, which are very low level compared to barefoot running. If he has anything like a rearfoot varus/valgus, forefoot varus/valgus, plantarflexed first ray, or even tibial torsion, he is at an increased risk of injury in daily life. Add BAREFOOT running (in someone who actually needs an orthotic to position them to maintain them out of their end range) and you just keep smashing them through their end range... that stretches structures unnecessarily and leads to pathology.
If you wanna know more about the conditions I listed, go here:
http://www.footmaxx.com/uploaded/product_category_pdf/file_22.pdf
It's kinda heavy on the nomenclature, but I think you'll get the info.