In Russian (yep, I'm originally from Russia) we are using term chemOinformatics, because it is rather sounds more correctly for the Russian-speaking audience. Because we already have chemometrics, chemotherapy that pronounce more like chimeotherapy, chemoreceptors - oldy term from 60, and many-many others where the sound O in chemO is connecting two consonant letters. That is also true for all the Europe and especially German languages as noted by Egon. The other point is - there is a word chemO that gave birth to many terms in English literature that are chemOgenomics, chemotherapy already mentioned, chemogenesis, chemoreceptors.
Despite typing cheminformatics that can save you 6.25% of typing time, I prefere to use chemoinformatics in unoficial communication, but cheminformatics in official.