Ive done it a similar method before. I have crimped them, then hold it in the vice as shown above and heat the connector to holy hell, then stick solder in the connection like you would a plumbing joint. The problem here, is that a lot of heat is conducted into the wire and melts the insulation too in my experience.
Typically, I just crimp them and call it good. Thats the way most aftermarket cables are if you think about it. Then again, it could just be to keep costs down. Ive used bulk solder and solder slugs before for cables too. I like the slugs better since you dont have to feed an entire roll in it seems, and they give you the same amount each time. Not to mention you can buy the exact amount for the number of connections, no guessing how many rolls of solder you need.
As for the crimps, Ive used both the fancy expensive crimpers, and the cheap "hit it with a hammer" crimper you can get just about anywhere, and both have worked for me.
At this point, Id say just run it and be aware they MIGHT give you trouble if you happen to create enough heat on the cable with a long winch pull, similar to melting a battery cable cranking a car that wont start, only faster because the winch pulls more amperage.
~T.J.
