Do these pertain to a players position or is it overall.

Example:
is a DT @ 100 speed as fast as a WR @ 100 speed
is a WR @ 100 strength as strong as a DT @ 100 strength?
Same for Intelligence?

Short answers
No
No
Overall
I may be incorrect but I believe intelligence is 'overall' but different positions utilise it in different ways.
Speed is based on the speed rating and weight not position ie DT and WR both 100 speed and 300 pounds = same speed but WR's are usually much lighter and therefore faster.
I am still little hazy on strength but i think two players same stats same strength then the 300 pound DT is going to knock a 190 pound WR into next week most of the time. But there are a lot of parameters in each position that will affect how well a player will utilise their physical characteristics.

Kind of a follow-up to this...

So I'm assuming Strength is important on the O-Line. But what's more important out of Speed and Acceleration? I mean, I've heard that Speed is crucial nowadays... But what's more important on the line: Being as fast as possible, or getting to top speed as quick as possible with so little space?

Is this the same thing on the D-Line as well?

Acceleration should trump speed on the line since there's no space really for a player to get max speed. If the DL ever drops into coverage (they do in some plays) then speed increases in value. Same with pulling blockers.

So basically Acceleration should be #1 priority, with Speed #1.5? Heh.

And does Strength apply in holding / breaking through a block? Or is it simply a momentum (Speed / Accel with player's weight) thing combined with the related 'Block' statistic?

Yes, strength is considered strongly (pardon the pun) in the length of time a block is held.