About to unlock this devotion but, I duel wield Marlee. Have I wasted my time with it or will it still proc with no shield to block with?
It proc’s on block and you can only block with a shield.
It only procs on block and you need a shield to block.
Are you dead certain about this as some Devotions state Shield required and the Anvil doesn’t have anything about Shield required, which makes it confusing, I’m going to ask elsewhere for clarification on this matter 
The ones like Shieldmaiden that “requires a shield” won’t even give the passive bonuses of the nodes if you don’t have a shield equipped.
Anvil’s passive nodes would benefit you without using a shield but the proc won’t ever go off as you won’t ever block.
I wanted to use it with my 2h melee Elementalist, but nothing happened when I assigned it to Primal Strike. Never went off so changed it for Owl instead.
Well that’s a bummer, seems to me bad guys can block without shields so we should too. After all a strike is a block and a block is a strike.
Only enemies with shields actually block. So no, enemies without shields can’t block.
Shields block. Weapons …well I guess they parry*, at best, in RL. ^^
ward off (a weapon or attack) with a countermove.
“he parried the blow by holding his sword vertically”
Synonyme: ward off, fend off, stave off, turn aside;
wut ? 
Very well points removed respec into wolverine instead.
In most basic fighting technique of just punch and block. If attacker throws a punch and defender blocks landing his blocking fist into attackers bicep with enough force to render attackers arm useless it is essentially a strike. Vise Versace if an attacker throws a punch can the defender not punch his arm away this an attack became a block. To master this and understand it concept ones complete movements becomes both offense and defense all the time.
Whether you want to put stock into any of that is up to you just something that was told to me a lifetime ago when I studied Isshin Ryu karate it stuck I suppose.
But alas I can not block with a mace and sword apparently making anvil unusable. Come on crate D2 had a passive to allow blocking whilst dual wielding claws.
The precise word you are looking for is “counter-attack”.
For ex. there’s counter-attack techique in boxing called “cross”. In fencing - “riposte/counter-riposte”. Etc.
To perform an offensive action for defensive purposes.
But a strike is exactly what it means.
Same for block.
Any word has certain meaning and use, you know.