There seems to be a historical or geographical connection between the various types of mercenaries you can hire in LOTR2 and where they're from.

For reference, when mercenaries are available for hire, they will be:

Archers from Mauritania or Wales
Pikeman from Scotland or Ireland
Macemen from Saxony or Burgundy
Crossbowmen from Flanders or Normandy
Swordsmen from Sweden or Denmark
Knights from Spain or Anjou

With the exception of the Moorish and Welsh archers, the mercenaries seem to come from regions that are pretty close together, though not adjacent. But despite the distance between Mauritania and Wales, it does make sense for archer mercenaries to come from one of those two regions, since both the Moors and the Welsh were well known for their archers.

But, for example, I don't recall reading anything about the Scots or the Irish being well known for their pikemen, nor the pike being invented by either of them. While the rest of the mercenary companies have some geographical consistency, are they historically consistent as well?

The Moors were not from Mauritania (not from where the present day country is). The term refers to people from Arab or Berber descent who lived in Iberia, the Maghreb, Sicily or Malta.

https://en.wikipedia.org/wiki/Moors

Isn't Maghreb another name for northwestern Africa (which the ancient Romans called Mauritania)? I know that the name "Moor" comes from the Latin "Mauri", which is what they called people from that area.

https://en.wikipedia.org/wiki/Mauretania

Yes, you're right. I just wasn't aware it's called so.

Thought Mauretania to refer to the modern country.

Scottish pikemen? Well i don't know, but going by the movie Braveheart, the scots invented some damn good spear units! lol

And since spearmen units are not in the game, then they had to make them pikemen? Or spearmen simply evolved into pikemen?

Correct. Because most pikes have spears on the tip of the shaft with the pike branching off to the side, it's as if you already have spearmen when you have a pikeman. It's like you're getting two for one. So the developers probably thought it redundant to use spearmen if they are already putting pikemen into the game.