Is per dium considered wages on long term travel assignments when figuring wages for workers comp?

It depends if it was an accountable or non-accountable expense. Accountable is not considered wages.

Accountable plan:
To be an accountable plan, your reimbursement or allowance arrangement must require your employees to meet all three of the following rules.
1) They must have paid or incurred deductible expenses while performing services as your employees.
2) They must adequately account to you for these expenses within a reasonable period of time.
3) They must return any amounts in excess of expenses within a reasonable period of time.

Non-accountable does not meet these criteria.