Never taken a knife to give as a tip. But over the years have given a few, in addition to cash, and they turned out to be pretty good gifts.
When those replaceable razor knives first came out the skinner/tracker was really taken with mine, so I gave it to him.
Year before last, skinner/tracker lost his while gutting an animal in the field. It had been given to him by a previous hunter. I had the identical knife with me (nothing fancy, a Gerber), and gave him mine. From his response, I think it was the best gift I ever gave in Africa.
I always carry a little Swiss Army knife with me. Everywhere. Mainly for the toothpick it seems. Those smallest ones with scissors and tweezers. Trackers this year took a liking to it. It t actually came in handy several times. Gave both trackers one at end of trip (because I always have a spare). They actually both acted like they appreciated them more than the money, and it was not a small amount.
I think the knives were good gifts in all 3 instances, but I think it had as much to do with the circumstances (or uniqueness in 1 case) and not just the giving of a knife.