"Stacking" bonuses usually refers to having them all active at once. By that definition, then no, it is not possible to stack the Monk and Swordsage ability - by RAW the condition to activate either one also deactivates the other.
A Monk only gains their bonus when not wearing any armor or shield. If they put on light armor (or heavier) their AC bonus no longer applies.
A Swordsage only gains their bonus when wearing exactly light armor (see note below). If they do not wear armor, or if they wear medium (or heavier) armor, their bonus deactivates.
Thus these abilities cannot be used at the same time, and do not stack.
However, if a multiclass character took levels in both Swordsage and Monk, they would gain both of these abilities, and whenever they were in light or no armor, the appropriate ability would be active.
Note: There has been a great deal of debate regarding the Swordsage's requirement to only allow the ability to work in light armor, and whether it was meant to be "in light armor or less". The only 100% official source (officially released Errata) does not discuss the swordsage's Wis to AC ability at all, so in RAW it remains in light armor only.
If you were to house-rule that the Swordsage ability should work when unarmored, then the abilities should stack fully. However, especially at low level, this has the potential to make for unreasonably high AC which will allow characters to breeze through combat. (Literally: all their enemies just keep fanning them off as they try to strike!)