It makes sense that once you've found your way round a fretted bass, playing on a similar scale fretless will be easier. But - violinists, cellists, double bass players, all start off with fretless, don't they?
Playing in tune is not easy on any fretless instrument, so it won't be as easy as on a fretted, but if you're willing to listen more carefully than someone playing a fretted bass needs to (!), then it's quite doable. There will be markers, but you'll have to decide whether they are at the exact spot you press for a note, or whether they're effectively in the middle of the 'fret', just as they would be on a fretted instrument. Little stick-on marks will help initially.
EDIT: Just realised that actually, apart from markers on and above 12th fret, the lower ones are pretty useless, as the parallax produced by the position of the bass' neck, and your eyes, means that they won't give a true positioning, as they can't be seen accurately to line up with anything tangible. This leads me to recommend a lined fingerboard for a beginner.