So your Dd's OH speaks to his recently bereaved mother every evening. Is that wrong? Quite frankly, I would rather be with someone like that , however annoying or frustrating it may be than he has no contact whatsoever - at least he cares.
I think that as they have been living together for 8 years, you can't really assume your daughter "puts up with it" unless she has actually stated this fact.
When you become part of a couple there has to be a fair amount of compromise on both sides or it will not work. Your daughter would have been aware of how close her OH was to his parents (guessing he's an only child) and so prepared .
There seems to be an idea amongst many people that post on this forum that when people become a couple, that both sides of their extended family will be treated the same - without both sides having exactly the same relationship, with their own families this is not possible.
In your case, at least your DD visits you. Some people are just not comfortable visiting people - however welcoming their hosts may be and in this case, you need to accept that is the way it is. If they both seem happy, just leave them to it. It is nobody else's business what goes on between couples unless it becomes an abusive situation.
Cut the poor guy some slack! If they want to get married etc, they will do, but in their own time - no guarantee it will make them any happier than they may be now!