-Can be compiled on any platform, including Windows, MacOS, Linux, Android, iOS, newer game consoles, etc. No other cryptocurrency can do this.
-Staking mobile wallets with transferable wallet.dat
-Only other coin besides BTC to require only 1 confirmation on Poloniex.
-Unlike Bitcoin, Vanillacoin's global transaction pool is highly synchronized, which makes malicious block reorganizations nearly impossible.
-Very active dev, most talented I've seen in the altcoin space.
I know the bitcoinj wallet has an online mempool it references from blockexplorers to find unspent outputs.. is it that?
It's not centralized, it's decentralized.
The dev has answered a few questions about it in bitcointalk. You can look through his posts or go on the Vanillacoin IRC and ask questions there.
Other than the source code, the proof is that Poloniex did a code a review and decided to lower necessary confirmations to 1.