I guess they're right that it would be weaker, but next time they tell you that - ask them what the rating is for a 7/16 grade 8 bolt, and a 7/16 grade 8 greaseable bolt. I'm sure they'd tell you that they heard it on the internet.
The grade 8 bolt has a shear strength of 7/16" grade 8 bolt is 36,000+ lbs (meaning, you'd have to hit a wall with your 2.5 ton FJ40 at 7.2g to get it to break)... drill an 1/8" hole in the middle and the bolt strength would, at worse, have a shear strength of 19,000 lbs. Thus, you have to hit something at 4g to break it. In either case, your issue won't likely be a bolt failing.
And with that said, each rear tire on a C2, C3, and C4 Corvette ride on a 1/2" lubeable bolt. (meaning it has a shear capacity of at least 38,000 lbs.)
tl;dr is if you size the bolt, increase the size by whatever the hole size is in the middle and you'll have the same strength as you with smaller bolt without the hole. There is argument that a hollow bolt would be stronger as long as you increase the diameter by the size of the hole.
with that said, with a lubeable bushing, you wouldn't need to worry about bolt strength.
*oh, and on a leaf sprung vehicle those fail numbers would at least a 1/3 low because there are 2 bolts per spring.