No, it isn't considered an SSRI. SSRI stands for selective serotonin re-uptake inhibitor or serotonin-specific reuptake inhibitor, which designates the mechanism by which this category of drug (supposedly) works: on the serotonin transporters in the brain. It's a term only used for a limited range of drugs, like sertraline and citalopram.
5-HTP (Oxitriptan being a trade name) is a chemical precursor to serotonin. The way it affects the serotonergic system is by increasing the rate at which it is generated. The category to which it belongs is the "serotonin precursor" category, similarly to e.g. L-tryptophan (which is actually itself a precursor of 5-HTP).
If it is prescribed to treat depression, it might be called an anti-depressant, but SSRI is a term for a mechanism of action moreso than an effect. Tetracyclic and tricyclic antidepressants, for example, also affect neurotransmitter uptake in the brain, but aren't called SSRIs.
Further reading: How Different Antidepressants Work