Ulcers in the mouth sometimes occur in overt AIDS
, due either to actual canker sores
or other problems that cause similar lesions. However, I stress "overt AIDS". This is not a symptom of early HIV; it is pretty much limited to people with multiple other manifestations of AIDS, mostly in people who are deathly ill. I have never heard of oral ulcers as the only symptom of HIV or of being the very first symptom.
So the direct answers are:
1) No, probably not.