So I tried exporting it to a pdf.
So apparently the correct color numbers are getting through, but InDesign and Acrobat flag 299% inks at 300%? What gives?
Same can occur in InDesign, they may be 1% off strange enough, but luckyly nothing to worry about ;-)
I agree with Frans total ink doesn't need to be that accurate—it's not like you will have a drying problem if the total ink goes from 300 to 301.
The default PS, ID and Acrobat separation numbers are not that accurate, an 8-bit per channel image can obviously have a lot more that 100 gray levels per channel. In InDesign you can spec percentages in hundredths, and you'll get hundredths if you convert an RGB or Lab color to CMYK. In Photoshop you can calculate tenths by setting the info to 32-bit and multiplying the readout by 100.