Actually, most Japanese maples naturally have a midseason growth spurt that typically occurs in late summer. It is NOT stimulated by fertilization and I wouldn't encourage any late fertilizing. Just plenty of water........and some judicious pruning......will help with a flush of new growth. However that growth does tend to be long and whippy and could experience some dieback in colder areas.

My Hupp's Dwarf is currently going through its midseason growth spurt, noticeable by the pink tips to the new growth. But because it is a true dwarf with very short internodes, it doesn't produce the typically long shoots at this time of year.

Thanks. Can I give it Dyna-Gro Foliage Pro or Miracle Gro liquid Fertilizer?

If growing in a container then yes, you would still need to fertilize as usual but you want to start tapering off next month.

Yes, there in pots. Would feeding them with Dyna-Gro or Miracle Gro liquid be better than applying Osmocote Plus this time of the year?

Yes, too late to use the Osmocote. Use the liquid/water soluble fert of your choice at half strength.