Hello eoniepony,
I usually recommend dividing the databases, to avoid accidentally using a cutoff process in a EN15804 system.
The two databases are fundamentally different, if only a little, in where their system boundaries are placed. When you make an assessment that has to conform to the EN15804 standard, you must use the EN15804 database, or another database that also fits the requirements in the standard.
When you make an LCA, PCF, etc. you can use cutoff.
If you do not use EN15804 processes, you will not be able to calculate EPD related impact categories, such as the ones regarding energy usage, inventory, and waste.
I hope this helps, best of luck.
