1. DVD-A does not allow you to create SVCD or VCD.
2. Your background video and audio have to be the same length to loop together. If the video is shorter than the audio, DVD-A during the disc build process will 'fill' in the gap so that the video will match the audio. Create your background video in your NLE with your audio file to be used to make sure the two match up and you shouldn't have a problem. This is a dvd spec limitation, and not a limitation of DVD-A.
As Jim said, DVD Architect will not do SVCD or VCD. Although DVD Architect has no official support for anything but DVD, it can save VIDEO_TS folders that can be burned by Nero to a CD-R to create a miniDVD. MiniDVDs will play in about a quarter of the current crop of DVD players, and they are higher quality than SVCDs since they have full DVD quality video and audio. A miniDVD is, in effect, a "tiny DVD" since it has the very same data structure as a DVD.
Since CD-Rs are so inexpensive, a 15-minute miniDVD can be very useful. Have you looked into the advantages and disadvantages of the miniDVD format? Have you determined whether your standalone DVD player can play miniDVDs? There is a lot of info on the www.DVDHelp.com website.
Don't forget, Vegas can burn VCDs (tools/burn CD/VCD), and has done so since V3. DVD Architect is just for DVD authoring, not SVCD, VCD, or the plethora of other CD-based outputs.