So I couldn't find anything in a google search about an athletics code of conduct at ISU, but apparently it does exist, as the following article in Athletic Management indicates, and it is apparently some sort of model, or was at the time of the articles publication (2010):
Athletic Management : Momentum Media
I was able to find an online copy of the UofI's policyon their athletics site, and we can probably assume ISU's is similar:
University of Iowa Official Athletic Site Athletics
One passage stands out, where the policy describes "Category I" offenses (serious) and differentiates them from "Category II" offenses. Basically, a Category I offense is one of three things: committing a felony, violating a court ordered probation or condition from a criminal proceeding, or violation of a probation or condition imposed by the athletics department. Category II offenses do not involve dismissal as potential sanctions.
One can probably infer from this that, if ISU's policy is similar to UI's, and we've not gotten word from the court that Bubu's situation has changed, that he likely didn't meet the conditions set by the athletics department for remaining a member of the team, if one assumes that such conditions were set when Bubu was reinstated last January.
It is important to note that there is a lot of supposition here, so be careful not to assume anything RE: Palo. But it is hypothetically possible for a player to be dismissed from a team without being found guilty of anything, provided they fail to meet the conditions set for them at the time they are re-instated.