As long as you SIGN UP for Serve through ISIS wallet (not ADD your existing Serve card to your wallet) you can load $1500/month. I added it in error so did my $1K 2 months ago, cancelled my card, waited the required 30 days and got a new Serve account through ISIS and all is fine.
And yes, I have loaded $1500 through my PC ($500 x 3) despite the fact $500 option is not showing in the add cash option. My guess is, just like AP, this will disappear shortly as well and I'm also betting Amex Sever is going to jump on the Apple Pay bandwagon.
I also discovered IOS 8 isn't compatible.