when I export from Inkscape (with the Inkscape addon svg2synfig) and then I open the .sif file with Synfig, the Animate button is not shown.
when exporting files from inkscape, you don’t get the time properties setup for you automatically
so then you’ll get a file with start and end time at frame 0
check the canvas properties (Canvas->Properties), then check the time tab and fiddle with it a bit
and this what happens when i set the start and end time at frame 0
notice that the time bar and animation buttons at the bottom are gone