There are a lot of things to consider when one-sided trades are accepted and simutaneously raises the attention of other league owners to its overall effect on the league as a whole. Especially this late in the season and close to the playoffs.
Are the two owners involved related?
From what you have stated so far the team recieving Foster and Welker is giving up a 2nd rd pick. Add in the fact that you mentioned also players that are kept lose the round said players were drafted in from the year before. So, I'm assuming Foster was selected in the 1st rd this year so the owner recieving him in this trade has already lost his 1st and 2nd rd picks for next season's draft.
You will have to give more info on this deal, including both rosters and the rds the players were taken in. On paper this trade is a fleece job for the team headed to the playoffs but until more info is given I can't quite confirm this deal is worth a veto outright. A good brow-beating on the league message board for sure, but hard to say collusion was involved solely based on the players involved and what little info you have surrendered here to date.