I understand that there is a tendency to "buy" a child's love out of guilt over a divorce. I think that my husband and my SD's mom do that sometimes, so that might be what you're sensing.
My SD received an American Girl doll when she was 5. She mistreated it and it is not in very good shape. Now she's 10 and she has 9 dolls and she treats them wonderfully. She is working to save her own money so she can get her mistreated AG doll a new head. She should not have gotten that doll at so young!
Her mom also bought her an iPod nano when she was 7. Not only did her mom put Explicit Lyrics songs on it (nice, huh? The f-word in songs for a 7-year old!) but my SD LOST the iPod!
The next year she got a new iPod (age 8) and then at age 9 they bought her a laptop computer! She has unrestricted internet access at her mom's. She's not allowed to use the laptop here, I won't allow her to surf the internet without an adult right next to her. She already googled the word "butt" as an innocent 9 year old might do and you can only imagined what happened!
So I'm right there with you, I understand in your situation how gifts like that can be inappropriate for their age.
That being said, my SD has a cell phone (so she can call us at her mom's house if she feels unsafe) and last year we got her a refurbished iPod Touch. I wanted her to have an iPod here that we could control the songs on it and the games. I know at her mom's house if they got her one they'd let her put anything on it she wanted and she'd probably end up with R-rated movies and songs! And that would be MUCH less age-appropriate!
Is your SD a responsible girl? Does she take care of her toys? Or will this end up scratched and tossed to the side?
I would say that either way, there isn't much you can do except let time tell. I didn't think the iPod was appropriate and my SD lost it when she was with her mom. Her mom was so mad! I didn't think the American Girl doll was appropriate and she destroyed that (it was at her mom's house so no blame here!) I didn't think the computer was appropriate and my SD rarely uses it. She even spilled pop on it when she was at her mom's house. Now that she's older I see that she takes good care of her phone and her iPod Touch, at least here she does.
Your husband will be the sorry one if she breaks it or doesn't play with it. So I'd just say your piece, and then let nature run its course!
Good luck!