If my father gives his grandson a $10,000 wedding gift months before he enters a nursing home, is that considered an asset transfer in a medicaid

If the gift was done in contemplation of becoming Medicaid eligible, then "yes" it will be considered as part of the Medicaid lookback.  I had a similar case in which mom and dad gave their daughter gifts of tens of thousands of dollars over the course of a few months so that she could pay for her wedding in California.  Shortly after the wedding the husband has a stroke and needed expensive long term care.  Medicaid considered the "gifts" to the daughter for wedding expenses to be transfers, but we were able to successfully fight that because of the wedding bills.  In your case, the $10,000 gift may result in one month of Medicaid ineligibility and you may be able to persuade Medicaid that it was not done in anticipation of your father going into the nursing home.