Are other Apple bands also compatible with the Apple Watch Series 5 Nike?

The physical Nike Apple Watch is physically identical the same model Apple Watch that is not Nike branded. The Nike gets a Nike ONLY watch band and a Nike ONLY watch face. Everything else about the hardware and software is the same as other Apple Watches.

Include the ability to customize your watch band.

That is to say, every 40mm (or 38mm) Apple Watch can use any watch band with that size specified. And every 44mm (or 42mm) Apple Watch can use any watch band with that size specified. Totally interchangeable.

When you say: "interchangeable" but within their size parameters? What I mean is this: the size of my wrist is somewhere between S/M and M/L. I ordered an original Apple sportsband for my 40mm Apple Watch 5 and there are two sizes in one package, as you will know. I'm most comfortable with the longest, the M/L so to speak.

But what if I order another band, either from Apple or not, would it be possible to order a 44mm band because they are longer than the 40mm equivalent? In other words, are bands meant for 40mm and 44mm (also) interchangeable? Are the bits that slide into the watch the exact same size?

You need a band that fits your watch's case. The 40 and 44 mm are not interchangeable, as one is meant to fit a larger watch and must occupy the complete bottom width of the watch. Any band that fits the 40mm watch only works with the 40mm watches, but are interchangeable between those same size watches. The same for the 44mm. On older generations with the 38 and 42mm watches. Hope this helps!

I understand now. Although the same system is used, I have to stick to 38/40mm bands that are made for my 40mm watch.

But just being curious, what would happen if I put a 44mm band on a 40mm watch? Would it stick out at the lugs? Would it even click to secure?

I've played with watch bands in an Apple Store and I've been able to put a 44mm band on a 40mm Apple Watch. The lugs stick out, but it does engage the catch mechanism.

The lugs sticking out can catch on your shirt, or other objects you brush your arm against.

The reverse situation of a 40mm band in a 44mm watch, the lugs do engage the catch mechanism, but the lugs do not full fill the case's watch band lug slot. There the worse that will happen is you will collect lint.