Maybe, but you're grading out nearly 400 players, if you take into account undrafted free agents. That's just not a specific enough system, unless you're taking a ton of people off your board altogether because... wait for it... you don't need them.
If you listen to a lot of football chatter, you might quickly find that scouting is really a six step process:
1) Regional scouts identify all the potential prospects within their region, and place an initial grade on them.
2) The scouts come home and are assigned a position group: one scout looks at all wideouts, one scout looks at all running backs, one scout looks at all QBs, etc. This is the positional cross-check.
3) Medical and personality checks are performed on the likely candidates for selection.
4) Some teams (the Cards did this under Graves) build a "BIG" board of all the prospects, and rank them against one another based on NFL value, which would be the presumed consensus of the NFL.
5) Teams then construct their own board, ranking each player against the others on preference of talent, fit for scheme, etc.
If there is over/underrating due to "need", I think it's largely subconscious. A player at a position that you need looks good, he's going to look even better, because you're specifically looking for those players.
To the OP, I don't think we'd reach for OL because it's a need--I think we can go to war with the guys we currently have on the roster. If we draft OL--particularly offensive tackle--we'll likely do so because that's the best player available.