This IS possible but requires careful planning in particular how the heating is piped and valved.
Any specific systems that you have in mind please provide sketches and advise can be given based on experience and practical application.
OpenTherm integration does vary in different boilers, particularly how stored hot water is implemented.
The prime thing is to keep the system hirachy as simple as possible without a 2 port valve on heating if possible.
Hot water priority can be accommodated depending on the boiler inputs.