Update:
According to this paper
http://www.inchem.org/documents/ehc/ehc/ehc204.htm#SubSectionNumber:4.2.3 regarding bioaccumlation in birds:
Pendleton et al. (1995) exposed adult male mallard ducks to a
dietary concentration of 1600 mg boron/kg for up to 48 days.
Equilibrium levels were reached between days 2 and 15. Boron
concentrations were highest in the blood, followed by the brain and
liver. Boron was rapidly eliminated, with few detectable residues
after 1 day on a "clean diet." The presence of arsenic (300 mg/kg) in
the diet slowed the accumulation of boron.
This dosage was much higher than that tested with dogs in the EPA studies referenced above in the link provided by Divin Dave.
I am extrapolating from ducks to bats and across species, but I have come to the conclusion that borates are safe for the bats skimming my pool. This is taking into consideration that the level at which dogs saw no adverse effect would equal a 1oz. bat drinking over 1/2 ounce of water and I don't think that any bat is drinking that much water from my pool.
I can keep my borates (which greatly helped with my PH stability and I noticed an extra "sparkle") without affecting the neighborhood bats skimming my pool for sips of water! We actually aren't putting the solar cover on the pool so the bats can drink...we'll get plenty or swim time soon enough.