Sorry, no. GarageBand on an iPad and GarageBand on a Mac are completely different programs. They need different processors and operating systems, and you cannot use an instrument update for the other platform.
The iPad in-app purchase will install very different instruments on your iPad - mainly smart instrumentsÖ
That is what you'll get on your iPad:
With a one-time in-app purchase, you can add Guitar Amp, Smart Keyboard, Smart Bass, Smart Strings, Smart Drums, Sampler, and a total of 157 preset sounds. The purchased instruments appear in the Touch Instrument browser after you purchase them.
On your Mac you got lessons, drummers, ans more sounds and loops: Expanding GarageBand for Mac (v10.0) content with an in-app purchase
With a one-time in-app purchase of $4.99, you can expand this content to 200 sounds, 2,000 loops, 15 Drummers, and 40 guitar and piano Basic Lessons. You will also gain the ability to purchase additional Artist Lessons.