Many families do share beds...its not that unusual and unless you think there is abuse ..I wonder why its inappropiate in your eyes .As you are concerned it may be aswell to speak to her Dad and find out if she would like to have a bed of her own ,what does your daughter say ?.
Sounds like you are considering two separate issues. One is the possible sexual inappropriateness of an 8-year-old girl sharing a bed with her dad. The other is that he is a big fat jerk who doesn't even care enough about his own daughter to give her her own bedroom, or is too obtuse to figure out the hidden needs of his daughter at age 8. Let's examine these two ideas separately.
By your tone, you don't sound like you think her dad is molesting her, but are beginning to get the idea around the edges that at some point soon, an opposite-sex child should not sleep in the same bed with the opposite-sex parent. You have lined up allies to concur, and are ready to hit him with the big gun if necessary, i.e., the portentious remark that this is sexually inappropriate behavior. However, if that was your only concern, you would be writing here about your serious worries, and whether you should ask the court for no overnight visits, or saying you want to demand he get a pump-up air bed for her (or him) to sleep on, on the floor, when she is there, to separate them. Because you aren't being this stressed and specific about the worried-about-inappropriate-sexual-issues direction, it doesn't sound like him doing something sexually inappropriate is the primary concern for you, even if it seems to you that sooner or later an 8-year-old should not expect to sleep in dad's bed when she goes over.
The second part, I watched when a divorced cousin of mine and his pre-teen daughter who sometimes went to stay with her mother. The dad's viewpoint was that his selfish ex-wife made their daughter feel unwelcome and unloved because the ex made her sleep in a tiny space that wasn't even a proper bedroom. This failure bolstered his opinion that the ex was a selfish, shallow, self-centered woman and showed what a sensitive dad he was. The only problem with this satisfying analysis on his part was that his ex-wife couldn't afford a bigger apartment while he (the ex husband) could, and he could also have helped his ex get a bigger apartment so their daughter would feel welcomed and supported in the vital issue of her own bedroom. Did he do this? No, he did not. His ex was involved with someone else, and he was darned if he was going to make her life more comfortable in any way. So, what suffering his daughter felt at having only her little cubby to sleep in went unaddressed in the war of righteousness between her parents. The girl didn't in fact act very unhappy in her cubby; it was close to the action and she could see what was going on in the apartment if her mom's friends were over. She did like going to see her mom, but the tension between her parents was tough on her.
By all means, ask your ex if he could make some kind of a plan or arrangement to create some privacy for your daughter, and maybe to do whatever is income-appropriate for him to give her a bed, or a room, or a blow-up mattress with a little tent top, or whatever he can. However, open yourself to the possibility (which might only be short term given her age) that maybe your daughter finds it safer or more comforting to sleep so near her dad when she goes overnight. Strange bedrooms can be alienating and scary to a kid, even ones that have proper clean linens and no clutter. They are not home.
My nephew is 8, and he often sleeps with his dad, it gives him comfort and he likes the contact. My sister is keeping an eye on the issue, thinking to hint her son out of the behavior sooner or later, but she admits there is little harm in it because it makes her son feel like he's on solid ground with the world every morning due to his dad's backup.
Anyway, go with your intuition, but please don't cloak the issue in the guise of your daughter if it really gets its emotional force for you because of what it says to you about your husband's character.