Yes, the Romans were rather tolerant of most religions that didn't preach outright revolt.
Yeah, I think that sums it up best. The Romans only really persecuted the Druids, and later the Jews when they engaged in rebellion. Christianity was kind of a special case, since while the Romans considered refusal to worship the Emperor to be treason, many Christians did not see themselves as rebels. They were generally willing to follow the law, they just refused to acknowledge the emperor as a god.
The Romans did not persecute Christians just because they practiced Christianity, they persecuted them because they refused to obey the emperor, which was treason. I think that this is an important distinction.
The Romans looked down upon many religions and/or discouraged them (Cults of Isis or Bacchus), but the empire only persecuted groups that it viewed as either a real or potential threat.