I would say proceed with caution... id personally not do it.
An adult angel with a young oscar - the oscar is a toddler, still quite stupid and clumsy, he could quite easily kill the angel accidently as a toddler would...
On the other hand, an adult angel is going to be rather experienced, but would probably only bully the oscar enough so that the oscar knows whos boss.
As soon as that oscar starts growing, and its temperment changes, who knows.