Ankit is actually incorrect about this. The fusion between Kami and Piccolo was indeed special. Nail clarifies that Namekian fusion is only possible between two Warrior Namekians when he says he's the only Warrior Namekian on Namek apart from Piccolo.
Kami is of the Dragon Scion Namekians, the ones that can creat dragon balls and are generally weaker than their warrior type counterparts. The fusion between Kami and Piccolo is a special one because they were originally one Namekian. Thus allowing them to fuse.
The normal Namekian fusion can be done for as many Warrior Namekians there are. But the manga establishes that Nail was the only Warrior type on Namek. Probably because Guru worried about the preservation of his race so he mostly made Dragon types as they are the only type that can produce eggs.
Funnily enough the guidebooks go against the manga as there is more Warrior types than just Nail.
List of references:
Chapter: 285 (DBZ 91), P14.2
Context: talking to Freeza
Great Elder: “Nail won’t be as easy to defeat as you imagine…He’s the only Warrior-type Namekian on this planet. Things won’t go as they have with the Namekians you people have killed.”
Chapter: 295 (DBZ 101), P1.4, P2.1-5, P3.1
Nail: “I-I’m astonished…I don’t know what kind of training you’ve done, but you’ve acquired unbelievable power…Still, it’s unfortunate…If you had only returned to the original, single Namekian you were, you might have been able to defeat even Freeza…”
Piccolo: “Are you saying that if I merged with God once again, my power would even surpass Freeza!?”
Nail: “Th-that’s right…I was overwhelmingly defeated by Freeza, but I should have a good comprehension of his abilities…[ ] So merge with me…! I’m also the only fighting-type Namekian on this planet…[ ] That’s right…Your power will become many times greater…”
Piccolo: “…You’re not lying, are you?”
Nail: “If you think so, you can just go get killed by Freeza…”
Translated Daizenshuu 4 excerpt
Incidentally the three "warriors" that attacked Freeza when he reached Guru's house was filler.