I have twice used a Walgreens gift card to purchase a WDW gift card.
I simply hand the WDW gift card to the cashier to ring it up, then keep my Walgreens gift card somewhat concealed in my hand as I scan it.
This doesn't give them the opportunity to say I can't do it.
It goes through with no problem, and I do not purchase any other items.
The registers allow the transaction.
Now, scanning two Walgreens gift cards for one purchase? Not so sure about that one.
I always cash out for a $50 card, which is an even trade for the WDW card.
I guess you could try it. Worst case, they see that you used a gift card on the first scan, and they don't allow you to complete the purchase.
If that happened, I would certainly argue the case, since the register will allow the first card to be applied, proving that you can use the Walgreens gift card to purchase the WDW card.
Good luck! Be sure to report back on how it all plays out, if you decide to try it.
ETA:
To answer your question, this is definitely not the best use of your points, since the higher valued cards cost fewer points per dollar.
However, if cashing in for the $25 & $10 cards is the best use of the points for your needs, then I would say go ahead with it.