No modifiers to the skill roll to tumble through an opponent's square when invisible by RAW.
From http://www.d20srd.org/srd/skills/tumble.htm :
DC 25: Tumble at one-half speed through an area occupied by an enemy (over, under, or around the opponent) as part of normal movement, provoking no attacks of opportunity while doing so. Failure means you stop before entering the enemy-occupied area and provoke an attack of opportunity from that enemy. Check separately for each opponent. Each additional enemy after the first adds +2 to the Tumble DC.
There are modifiers given at that link based on terrain that may increase the DC, but no bonuses to skill rolls or reduction in DC due to conditions on the tumbling character.
Visually undetectable. An invisible creature gains a +2 bonus on attack rolls against sighted opponents, and ignores its opponents’ Dexterity bonuses to AC (if any).
A DM might grant you that +2 on the Tumble roll instead, although that is not listed as a specific benefit anywhere. It would seem to come under the "if it's not in the rules, but seems to give an advantage, grant a +2" advice in 3.5E - technically this discretionary bonus is RAW, but it would have to be discussed at the table.
Note that if you do fail the check to move through an opponent's square and provoke an attack of opportunity, the opponent will not be able to take it, as you still have Total Concealment, which grants this:
You can’t execute an attack of opportunity against an opponent with total concealment, even if you know what square or squares the opponent occupies.
So being invisible is still doing something for you here - it removes the risk associated with failure.