OpenEMR now codes to produce the X12 standard, which has been in force as the replacement for 837P since the introduction of the NPI. ALL the fields are being required by some payers, while others are using only some of those. But they still work with the rest of the data.
There have been some specifics which have had problems, but those have been addressed in the forums to fix on a "per payer" basis within the php coding.
As of right now the remittance handling is manually entered using the EOB in the Billing section. Hope that helps. Please let us know what version you are using and the OS platform you use as well in future to help us help you. Thanks.