How well do reflowed connectors self align?
I would either ask the manufacturer for an app note on the subject, or I would choose a different connector with alignment pins.

Not to belittle anyone on this web site, but unless someone here can give you the exact PCB footprint that they used on that exact connector, the exact make/model of solder paste, the exact dimensions for the solder stencil (width, length, and thickness), and the exact temperature profile for the reflow oven then I wouldn't trust their information.

The problem is that the dimensions of the PCB pad, and how the melted solder flows on that pad, will effect the self-aligning process.  More or less solder will effect things.  Different solder alloys will effect it.  Etc.  Just knowing that this guy was successful isn't enough to guarantee that you'll be successful.  You need to know everything to a precise degree, and I honestly doubt that anyone here will be able to give you that level of detail.

So...  Talk with the manufacturer.  If they want to sell you stuff then they should be able to help.  And if they can't, then use something else.