Palm mulch is OK, as long as it's composted down quite a bit, which it sounds like your supplier is providing.
But if you get a load of wood chips directly from a tree trimmer, and they've run palm branches through the chipper, it's hell to try to shovel and move. Palm is stringy and tangled. It's horrible to try to put a pitchfork into a tangled pile and transfer it into a wheelbarrow. Imagine trying to pull one strand of spagetti out of a big pile of cold noodles --- impossible. Digging into a pile of chips where there is tangled palm shreddings interwoven is horrible. I've learned that lesson multiple times, yet I still forget to ask sometimes and then I get a tangled mess dumped in my driveway. It takes twice as long to move.
It sounds like your potential source has composted and screened stuff to work with. That'll be easier, but of course, expensive. Given the fact that its already composted a bit, it'll break down very quickly and you'll be left buying 10 yards more next year. Raw wood chips take that much longer to break down.
Can you cut out the middle man and just find non-palm chipped tree trimmings and get them directly delivered to your place? You'll compost them yourself, simply by laying them down on the ground. Further, with the strong winds out in the Coachella Valley/Palm Springs, I'd think that heavier non-composted chips would be better. Finer compost will blow around.
I don't worry about about alleopathic trees -- it all breaks down and those chemicals disappear. In our area, that would be eucalyptus. Just pile it up for a couple of months if there is a question, or don't put it directly on beds you are seeding. It'll be fine around established plants and trees.
I have used palm fronds directly on the soil with chips piled over the top of them. They'll break down in less than 2 years if you bury them in 8 inches of chips. But if you're planning on digging through them, they're a pain in the ass. I have a hillside that is planted with an orchard. I pile palm fronds and other branches on the downhill side of the tree, building up organic terraces below them (which is also the south facing, sunny side). Over the years, those mulch piles have broken down beautifully. I cut down 6 VERY tall queen palms and all that biomass went on those mulch piles. That was 5 years ago. Today, you can't find any of those branches or even trunks --- it's all humus.
I've also used palm branches and trunks in
hugel beds. Bury them a foot below the soil surface and they'll break down quickly. AMAZING
water retention and fertility, but it took 2+ years.
The key in your climate will be to keep that biomass reasonably hydrated. If it stays moist, it'll break down and
feed your soil. But if it dries out (as is the case in the desert), it won't break down and feed the soil.
Best of luck.
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