Looks like you can't actually capture or make the dreadnought.
Nope! Like the Remnant Nexus, it's there solely for the player to fight.
When you spawn it in to your fleet, is it possible to have it spawn with the bow? Or some how attach it?
You're spawning the wrong variant with Console Commands. Again, like the Remnant Nexus, there's a damaged and a complete version. Use 'list variants' to get a complete list and find the version ('Standard') with the bow (the issue is that the damaged version is the earlier one alphabetically, and so it gets picked when you spawn just the hull without specifying a variant. Module ships; not always 100% user-friendly behind the scenes).
(In case Harmful Mechanic reads, I thoroughly enjoy your mod and can't wait to see what you have in store next!)
I've got an entire unreleased mod to finish up! I've been busy in quarantine. But this one is due for a big update full of love, too. I've been making good progress on both.