I can't say I know very much about them either

I believe though, that one of the reasons for the use of pikemen was that the Swedish army consisted of far more cavalry than was usual by that time (50% of the Swedish army was cavalry by 1701!) and while the russian army was more regular in it's proportions I suppose that considering the size of that army they still had quite a lot of cavalry for the Swedes protect against

Also I suppose pikemen are cheaper than musketeers as anti cavalry protection...
I found this when searching for "great nordic war tactics":
http://www.algonet.se/~hogman/stridsformeringar.htm
The text there is in swedish, but should you want to look at the pictures, the red squares are pikemen, the light blue are grenadiers and the green ones are musketeers (the dark blue picture at the bottom is a cavalry formation).
It seems that basicly there where half as many pikemen as there where musketeers in a regiment (same is true for a company).
Pikemen and Musketeers fighting together:
The only reason I mentioned it is becouse I know they where somewhat effective and either the pikemen should still be good enough to tackle State commisioned cavalry, or there should be a more modern pikeman.
While searching I also found this picture:
Which would seem to imply that Prussia also used pikemen during the 18th century (acording to the text under the picture the soldier is from 1756).
If you have problems with unit slots though I don't think it'd be too horrible if you left this kind of unit out, of the nations in this scenario only one seem to have used pikemen by 1700
