Totally depends. An appropriately chosen item (age appropriate, without any controversial possibilities?) would be fine. But, to say... promise a TV for their bedroom? Um.. NO.
Just a toy? Sure.. go ahead. Even a messy toy. Or a noisy toy. But a shootem up PS3 game rated M? ---you'd better check with me first.
If the gift is something that there is a lot of controversy around (toy guns for example---which I am fine with, but some aren't, and I wouldn't give one without asking the parent, if I didn't already know their position on them) then I would expect to be approached in advance. If it is a family member who knows our particular quirks or whatever, and wants to gift something they know is outside of what is generally acceptable in our household, then yes, I'd like them to ask me about it first. If it is something of a religious nature, then unless we share the exact same religious faith and practice, then I'd want you to check with me first.
A Disney movie, a package of playdough, an art set, a chalk board, dress up sets, etc...? Who cares...