Not simultaneously, but either or.
To clarify... a bcdc25 can take 25A from a source, alternators can do this. For solar a 200W panel will supply about 10-12A at best case. An external changeover relay will provide solar in the absence of alternator feed, the new dcdc with inbuilt changeover selects the higher current input. Voltages are different too, the inbuilt mppt controller takes full solar voltage which is probably 16 or 17V, OC voltage around 21V... alternator is maybe 14V, depends on age and brand etc.