Well, the start pages states "Vector maps from OpenStreetMap" 3 times. Technically it is up to app developer to add proper attribution, as our SDK can be used with other sources also. OSM is provided just for convenience. But point taken, I'll add reminder about attribution requirements to the developer guides also.

The developer portal at https://developer.nutiteq.com mentions OpenStreetMap, but the start and product pages doesn't. No link either. Perhaps you provide more sources, I haven't looked into the product very carefully. Your support told me OSM is used as map data source, didn't mention any other source. My understanding of the OSM license agreement is that you have to make it more explicit. But I'm no lawyer.

"Our requested attribution is "© OpenStreetMap contributors". You must also make it clear that the data is available under the Open Database Licence. This can be achieved by providing a "License" or "Terms" link which links to www.openstreetmap.org/copyright or www.opendatacommons.org/licenses/odbl."

Regardless whether required or not I think it'd be cool of you to mention it more explicitly since you're creating a business around it.

Sure, I'm daily OpenStreetMapper myself. The other map options can be added in project basis, as the geodata from any other sources tends to be extremely expensive for average end-user app developers. Of course it has to be attributed properly in each app.

Still, you should mention it (prominently, hopefully) on your homepage.

I don't think it'd hurt your business, quite the opposite. For some people, knowing it's OSM-based may be a feature.