The rating of D Connectors varies considerably with price, quality, manufacturer and construction.
As has been mentioned, a typical connector you might obtain from a model show or shop is unlikely to have a sufficiently high current rating for DCC.
However, better quality types can be found, rated at 5A per pin if you can justify the cost.
Alternatively, you can use more than one pin for each connection to spread the current if that suits you instead (usually adjacent pins would be used for convenience). Even military equipment sometimes uses this technique to save having to use special mixed contact connectors with their even more horrendous price tags!
Heatshrink over each joint is definitely worth the effort to reduce the risk of shorts occurring should any strands come loose (which they shouldn't, but it can happen).
Most people shy away from using 50 way D connectors though, because they have three rows of pins and it can be difficult to access the middle row for maintenance should it become necessary.
As has been mentioned, a typical connector you might obtain from a model show or shop is unlikely to have a sufficiently high current rating for DCC.
However, better quality types can be found, rated at 5A per pin if you can justify the cost.
Alternatively, you can use more than one pin for each connection to spread the current if that suits you instead (usually adjacent pins would be used for convenience). Even military equipment sometimes uses this technique to save having to use special mixed contact connectors with their even more horrendous price tags!

Heatshrink over each joint is definitely worth the effort to reduce the risk of shorts occurring should any strands come loose (which they shouldn't, but it can happen).
Most people shy away from using 50 way D connectors though, because they have three rows of pins and it can be difficult to access the middle row for maintenance should it become necessary.