In FontLab, if the font has kerning and classes (defined in Classes panel), it’s what we call “visual kerning”. If you don’t have visual kerning in FontLab, but you have a “kern” feature, in FontLab 7.2, use Font > Kerning > Import from [kern] feature.
The rest mostly depends on whether the source is single-master or multi-master, but it’s generally better to only use the visual kerning and remove the “kern” feature.
When you export that source file as a .glyphs file, FontLab will export the kerning and classes in a Glyphs-compatible way.
For multi-master sources, keeping the “kern” feature in the feature definitions does not make much sense at all. For single-master sources, it also is not necessary. You can remove it in FontLab’s Features panel, or later in Glyphs Font Info.