Yes, but you have to do it within 30 days of the marriage. This presumes you are talking about Employer Group Insurance. For more details see http://www.steveshorr.com/late.enrollee.htm
http://www.dol.gov/elaws/ebsa/health/11.asp
Spouses are allowed to carry separate insurance policies, as there are no laws stating otherwise. However, it is generally more cost effective for spouses to carry one together.
Credit Life Insurance.
yes
It does. Beginning June 26, 2013, same-sex spouses of active service members are eligible for health insurance.
Yes, they do.
No, most states require that pre-existing conditions be waived when moving from a group policy to a group policy. Pre-existing condition clauses apply when the break in coverage is greater than 63 days.
yes they can
Yes, they do.
Generally, the owner of the policy has the right to choose their beneficiary.
They can choose not to provide coverage for a spouse. US law states employers have to provide insurance for employee's children under the age of 26, but does not say anything about spouses, so they can choose to stop covering employee's spouses.
There can't be a way for it to be held against YOU. Other insurance companies can't bug you for their mistakes.
Not in the United States or Canada, unless the employer also refuses insurance coverage to opposite-sex spouses.