Stephen is correct. The IMB (and the FMB, as it was previously known) has always required believers' baptism by immersion (which is to say, it is a distinctively 'Baptist' mission organization). The new policies not only require believers' baptism by immersion, but by a minister and church who explicitly hold and teach particular doctrines, namely, eternal security of the believer and that baptism as an act is not salvific. Even if a missionary candidate believes these things while the church baptizing them does not, their baptism is considered to be invalid. This stance marks a clear departure from historic Baptist positions on both the autonomy of the local church and the accountability of every soul before God.

I don't think that you have Hammer's problems with the IMB rules on baptism quite right. I don't think that he has any problems with requiring believer's baptism by immersion. "The new missionary candidate policy regarding baptism goes beyond the above consensus doctrinal parameters of the SBC, and Scripture, adding extra-biblical stipulations concerning the church and administrator of the baptism. It also puts the IMB in the place of the autonomous, local Southern Baptist church in determining the validity of a candidate’s baptism…and worse than that insists to some that they re-baptize the missionary candidate. Organizational compliance is not a biblical reason for baptism or rebaptism. A Southern Baptist church member whose baptism by immersion, after regeneration, in obedience to Christ and as a testimony to their faith in Christ was accepted by a Southern Baptist church should be acceptable for service in a Southern Baptist entity or agency."