Natural occuring asteroids are probably harder to detect against the background noise than a directed attack with "fleets" of kinetic weapons.
But then: If you are willing to wait the the immense time span between attack and defence it might be feasible to build stealth-missiles and just fire them conventionally. At that speed a well built missile would have a devasting impact on a planet not militarized, not rugged planet - and can be stealthed by conventional means of decreasing radiation signature/refraction of incomming radiation.
But waiting 400 plus years just to spell silent doom to planets you haven't really charted and must hit with relative pinpoint accuracy is hardly something you want to rely on.
After all, a weapon your enemy won't fear for whatever reason is not really helping out any wargoals you might have.
If you use it as a measure of diplomatical engagement with the umiak the umiak might just prepare for that kind of attack or even preemptively retialate to gather enough intel to make the defence reasonable unexpensive. But maybe mankind will side with Umiaks and is looking for a way to destroy the loroi race? At least they can display their mind-reading-blocking abilities then
![Smile :)](./images/smilies/icon_e_smile.gif)
About the ftl idea:
As far as i visualized it, when you enter hyperspace with your bubble, you have "hyperspace momentum" which pushes you father away from real-space. If that force isn't counteracted you will remain in hyperspace forever (at least in real time... maybe you get flushed back when the underlying space as "reticuled" by matter ceases to exist?)
So for FTL drives to work you desperately need a "heavy" target to attract you back into real space-time. Plotting a vector without any heavy objects in the way will not only be risky it will fail every time. Also FTL incursions into star systems can be tracked in an unexpensive way if not obstructed by other radiation i guess.
Another idea i want to promote.
Use of short range ftl drives for the use in capital ship missiles.
It might be possible (with enough finesse in ftl engineering) to just phase out a missile and vector it to the next largest enemy mass concentration on the battlefield either deploying a conventional warhead or kinetic energy, bypassing any point defence systems on their way.
What about even smaller scale "hyper-ballistic" weapons... if the computation power and technical prowess are reasonable high it might be possible to create hand held hyper-space ammunition allowing to negate ground armor and heavy planetside fortifications by just re-entering real space-time at approbriate distances.