My BD supports XviD and MKV formats (it doesn't specify what the MKV should contain - which is useful - not)
If it says MKV container then it will normally be any codec that the player hardware can normally handle.
For playing DVDs this means MPEG1/2 and for BR this is MPEG4 ASP and AVC.
MPEG4 Part 2 of the specification is ASP, (Advanced Simple Profile), which is the coding specification XviD uses.
MPEG4 Part 10 of the specification is AVC, (Advanced Video Coding), which is h.264, which is a codec normally used for Blu-Ray.
Therefore, if the player can handle Blu-Ray, then by inference it can handle h.264 and because it states it can handle the MKV container format, then by extended inference it can handle h.264 within that container. It will also handle MPEG4-ASP, (XviD), format video within a MKV container, (as well as an AVI container which is what they're implying by simply stating "XviD").
An easy way to test is just do an encode of a small video using VidCoder and see if it plays. If it's a really small video, don't blink or else you'll be wondering if it did it