Those nodes hardcoded in the wallet sound like seed nodes to me.

Masternodes are nodes which enable instant transactions and the people operating them get a percentage of the tx fee. They need to hold however a certain amount of coins as collateral to qualify as "masternode".
I don't remember which coin had those first (Dash?) but since then every coin and its dog goes that route. Because a) it enables people to earn interest with a (Pos-free) PoW coin and b) it locks the collateral which means it cuts the supply on the exchange, resulting in an artificial price increase.

From what I understand Iridium does not have masternodes on the roadmap, neither are they being worked on.

If anyone can come up with a good argument why masternodes make sense technically in a coin which can do the mixin without masternodes, please do so.