Think of the physics involved, an off-set rim places the tire further out, or spacers put it further out. If a spacer is detrimental to bearing life, so is an offset rim. Same thing.
X2
You said this was a 99 Explorer unltd 4X4. Remember your Bearings are a one piece Hub setup, structurally MUCH weaker than a 1st Gen with the DBL Wishbone setup, which has spindle bearings.
I have seen spacers and offset rims destroy hub bearings. They are not designed for the amount of leverage applied by your rims/spacers. It increases the vertical leverage about 10X for 1 inch of outward movement.
Those bearings arent cheap...
Remember how your vehicle was designed to work and take into consideration the changes you are making and what they might cause to other components.
This is not to say its a bad Idea, just to warn you not to do it without thinking of everything.
I will also say I ran 10" wide rims and 33's on the Mutineer for YEARS and had no bearing issues, and I used the HELL out of it.
...so its a 50/50 chance... Im not sure exactly how your bearings are, but Ill bet they are close to how mine were.
my motto is Go before Show, Definately go with the wheels, they will be built to balance the weight whereas spacers just push everything outward and create more leverage.
IMO - I would definately
NOT recommend spacers of any size except on maybe a 4-wheeler or something.
For an example I will show my Dodge Ram in the pics below(same type hub bearings). This is back a few years, when I was all about the wider, more aggressive look and didnt think about the consequences. I replaced my 3rd set of hub bearings in a year, and upgraded to less backspacing and 33" Bias-Ply tires. I could have gotten 10" rims that were built for my truck but these were cheaper (in the short run).
I was driving down the road at 45MPH when it went, so it tore up all kinds of stuff and I barely missed an oncoming car.
Dont end up like this: