Hey Brent,
No, I've not actually implemented it yet, just read up about it really but it's something I intend to do as I've SO many shirt designs and graphics that have never been used through working or a few labels in the past and doing my own stuff.
The way I'd envisioned it was to make a stand alone site and then attach Shopify which is cheaper if you have your own site/hosting and then link it to a drop shipper like Printful.
Many drop shippers will do white label with no reference to themselves and also put your branding on the delivery label so it appears that the product has come direct from yourself.
Some will even put some stuff that you provide in there like freebie stickers or whatever you want for a fee as long as you're making a certain number of sales.
They tend to work by charging you for the cost of the garment/printing and postage and you set your own price above that.
When I say "niche" it was more in the way of a lifestyle brand or label.
One being a bit of a JDM, graff, skate vibe and another that is more mid century, hot-rod, tattoo and motorcycle inspired.
Financially, there is little risk as all you pay for is your hosting, Shopify, promotion and any paid ad's if you want them.
If you check any of the large drop shippers out they usually have explainer vid's about how it all works.
Too good to be true? Probably but hey....Nothing ventured.
I've only got as far as making a bunch of designs and branding but I did make a video teaser for one of them while I was playing with After Effects.