As a purely academic matter, there's a big difference between offering to pay any hit-related fine before the hit is actually made - versus after. If the offer is unknown to the player at the time of the hit, it hasn't been incentivized. But in reality, I'm sure the league would frown upon any such offers. So no, it's not a bounty or anything like it (if the offers aren't made until after the hit).
The comments by Lewis and Bruschi, IMO, are just hot air on TV . . . I don't think they actually intend to give Brooks any money if he were fined (and the league certainly wouldn't accept payment from some other person besides the offending player). Unless this becomes actual (the offeror does give money to the player) or a common occurrence, I don't think the league will do or say anything about it.
Is it bad form on the part of Lewis and Bruschi - guys who have no part in officiating, rulemaking, or discipline - to make those statements? I think it is.