There is clearly a correlation between policy positions and campaign contributions. Officials whose policy positions are in line with the preferences of a given interest group are much more likely to receive contributions from those groups. What this means is that interest groups are more likely to give money as a reward then to those that vote with them than they are to give money in an attempt to persuade those that tend to vote against them.
This is not to say that officials adopt policy positions in order to get contributions. That may happen, but it is also likely that most officials take positions that they believe in and are then supported by interest groups who approve of those positions.