Scotchloks work in a pinch but aren’t recommended and it makes the install look ugly. That being said, you can absolutely negotiate 1gbit full duplex without any errors, and the cable will be fine to use. I’ve used them in situations where I had nothing else and needed a halfway decent connection. I’ve also tested over cabling terminated with Scotchloks with a tdr and they show no difference or reflectivity along the wire. It could be worse, they could’ve used wire nuts. Or used cat3.